Bundle the extension using esbuild

[marcfrederick]

Adds bundling using esbuild to the extension. This should lead to improved performance and decrease the total size of the extension.

$ du -h bundled.vsix
532K    bundled.vsix

$ du -h unbundled.vsix
1.3M    unbundled.vsix

Previously vsce would complain when packaging the extension:

This extension consists of 1192 files, out of which 1127 are JavaScript files. For performance reasons, you should bundle your extension: https://aka.ms/vscode-bundle-extension . You should also exclude unnecessary files by adding them to your .vscodeignore: https://aka.ms/vscode-vscodeignore