feat: multi sketch folders support

[dankeboy36]

This PR supports multiple sketch folders opened in the same workspace.

Although the Arduino IDE can open only one sketch at a time, no technical obstacles exist to support multi-root workspaces with any number of opened sketch folders in a single (Arduino IDE, VS Code) window.

Added:

• get the current sketch,
• receive an event when the current sketch changes,
• get all opened sketch folders in the window,
• get an event when the opened sketch folders change,
• receive an event when the data folder (directories.data) or sketchbook location (directories.user) changes,
• receive an event when the selected board, port, etc., per sketch changes

Changed:

All existing APIs will be deprecated but kept backward-compatible!

• deprecate existing APIs,
• merged the boardDetails and the fqbn into board:
  • when no board is selected, it's undefined,
  • when the board is selected, but the platform is not installed, only the board name is available: { name: "ABC", fqbn: undefined }
  • when the board is detected on a discovered port, but the platform is not installed, it's { name: "ABC", fqbn: "a:b:c" },
  • when the platform is installed, it's a complete BoardDetails object with the fqbn, name, programmers, etc.

Tests:

• nyc coverage in VSIX tests. Thanks for the great post, @frenya ❤️

TODOs:

• Document + test API migration. For example, use context.currentSketch?.board?.fqbn instead of context.fqbn.

[dankeboy36]

🎉 This PR is included in version 0.2.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release
• Visual Studio Marketplace
• 0.2.0

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