Fix issues with opening links and files using WSL

[bottino]

• PR Description

This PR fixes to issues with the current implementation of the OSConfig for WSL:

File explorer
When using the file explorer from WSL, for instance by pressing "o" in the "Files" menu, the explorer always opens on the default landing page. This is caused by the filepath being expressed in WSL format instead of the expected Windows format. For instance:

• "/home/myuser/path/to/my/file" should be "\wsl$\MyDistroName\home\myuser\path\to\my\file"
• "/mnt/c/path/to/my/file" should be "C:\path\to\my\file"

There's a utility to do that in WSL, wslpath. We use it in the Open to format the filename before passing it to the Powershell command

Link URLs
Opening links containing ampersands inside lazygit (a pull-request creation page in BitBucket Server, for instance) returns the following Powershell error:

The ampersand (&) character is not allowed. The & operator is reserved
for future use; wrap an ampersand in double quotation marks ("&") to
pass it as part of a string.

We fix it by enclosing the URL in single quotes.

Notes on this PR
This is my first PR on this repo, please tell me if something is needed. I read the contributing guide.
The OS-specific logic doesn't appear to be tested in integration and unit tests, so I didn't add tests.

• Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc

[bottino]

As an alternative, we could default to using xdg-open for all Linux systems, and refer WSL users to wsl-open.

[jesseduffield]

I'm not well versed in WSL but I trust your reasoning.