Support '.jsonc' file extension for files inside '.vscode'

[kripod]

Currently, parsers struggle to read JSON comments when coming across the '.json' extension. Using the '.jsonc' extension implies that the given file is allowed to have comments, e.g.:

.vscode/extensions.json -> .vscode/extensions.jsonc
.vscode/settings.json -> .vscode/settings.jsonc

As a temporary workaround, a .gitattributes file like below could be used to signal GitHub's parser that files inside the '.vscode' directory use JSONC syntax:

.vscode/*.json linguist-language=jsonc

[joaomoreno]

Closing this down. If this is useful, just create a PR for it and ping me in it.