Rename font assets when theme is saved and/or exported

[matiasbenedetto]

What?

Fonts asset files added to the theme are renamed with a human-readable name.
No functional change was added.

Why?

To make the files easy to identify.
Fixes #710

Example

Before the resulting theme.json looked like this:

 {
                    "name": "Abhaya Libre",
                    "slug": "abhaya-libre",
                    "fontFamily": "\"Abhaya Libre\", serif",
                    "fontFace": [
                        {
                            "src": "file:./assets/fonts/e3tmeuGtX-Co5MNzeAOqinEgfkPWovdU4w.woff2",
                            "fontWeight": "400",
                            "fontStyle": "normal",
                            "fontFamily": "\"Abhaya Libre\""
                        },
                        {
                            "src": "file:./assets/fonts/e3t5euGtX-Co5MNzeAOqinEYj2ryr9xI6oYtBA.woff2",
                            "fontWeight": "500",
                            "fontStyle": "normal",
                            "fontFamily": "\"Abhaya Libre\""
                        },
                        {
                            "src": "file:./assets/fonts/e3t5euGtX-Co5MNzeAOqinEYo23yr9xI6oYtBA.woff2",
                            "fontWeight": "600",
                            "fontStyle": "normal",
                            "fontFamily": "\"Abhaya Libre\""
                        },
                        {
                            "src": "file:./assets/fonts/e3t5euGtX-Co5MNzeAOqinEYx2zyr9xI6oYtBA.woff2",
                            "fontWeight": "700",
                            "fontStyle": "normal",
                            "fontFamily": "\"Abhaya Libre\""
                        },
                        {
                            "src": "file:./assets/fonts/e3t5euGtX-Co5MNzeAOqinEY22_yr9xI6oYtBA.woff2",
                            "fontWeight": "800",
                            "fontStyle": "normal",
                            "fontFamily": "\"Abhaya Libre\""
                        }
                    ]
                }

After the resulting theme.json looks like this:

                {
                    "fontFace": [
                        {
                            "fontFamily": "\"Abhaya Libre\"",
                            "fontStyle": "normal",
                            "fontWeight": "400",
                            "src": [
                                "file:./assets/fonts/abhaya-libre-400-normal.woff2"
                            ]
                        },
                        {
                            "fontFamily": "\"Abhaya Libre\"",
                            "fontStyle": "normal",
                            "fontWeight": "500",
                            "src": [
                                "file:./assets/fonts/abhaya-libre-500-normal.woff2"
                            ]
                        },
                        {
                            "fontFamily": "\"Abhaya Libre\"",
                            "fontStyle": "normal",
                            "fontWeight": "600",
                            "src": [
                                "file:./assets/fonts/abhaya-libre-600-normal.woff2"
                            ]
                        },
                        {
                            "fontFamily": "\"Abhaya Libre\"",
                            "fontStyle": "normal",
                            "fontWeight": "700",
                            "src": [
                                "file:./assets/fonts/abhaya-libre-700-normal.woff2"
                            ]
                        },
                        {
                            "fontFamily": "\"Abhaya Libre\"",
                            "fontStyle": "normal",
                            "fontWeight": "800",
                            "src": [
                                "file:./assets/fonts/abhaya-libre-800-normal.woff2"
                            ]
                        }
                    ],
                    "fontFamily": "\"Abhaya Libre\", serif",
                    "name": "Abhaya Libre",
                    "slug": "abhaya-libre"
                },

How to test

Testing 'Save theme' workflow:

1. Create a blank theme using CBT.
2. Install a few fonts using the Font Library
3. Save the theme and inspect that the font files in /<theme-folder>/assets/fonts/ have human-readable names.

Testing the 'Export theme' workflow:

1. Create a blank theme using CBT.
2. Install a few fonts using the Font Library
3. Export the theme and inspect that the font files in the resulting zip archive have the fonts in /<ztheme-folder>/assets/fonts/ featuring human-readable names.

---

Related pending issues that aren't part of this PR:

• Add fonts to theme assets when a style variation is created. #695
• Update PHP tests to follow WP core conventions. #666
• Improve the CBT_Theme_Fonts class tests #711

[matiasbenedetto]

Updated the code to put the fonts into font-family sub folders.
Example:

                {
                    "name": "Alef",
                    "slug": "alef",
                    "fontFamily": "Alef, sans-serif",
                    "fontFace": [
                        {
                            "src": [
                                "file:./assets/fonts/alef/alef-400-normal.woff2"
                            ],
                            "fontWeight": "400",
                            "fontStyle": "normal",
                            "fontFamily": "Alef"
                        },
                        {
                            "src": [
                                "file:./assets/fonts/alef/alef-700-normal.woff2"
                            ],
                            "fontWeight": "700",
                            "fontStyle": "normal",
                            "fontFamily": "Alef"
                        }
                    ]
                },
                

[jffng]

LGTM, tested both saving and exporting with multiple fonts added to the theme works as expected.