Enable workspace file extension customization

[msujew]

What it does

As of now, only .theia-workspace and .code-workspace files are supported when selecting/creating workspace files. This change allows to easily customize the workspace file extension and also to exclude .code-workspace files.

How to test

1. Change the WorkspaceFileService#getWorkspaceFileTypes method to return a different array.
2. Assert that services that interact with workspace files adapt as expected.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[tsmaeder]

@msujew what problem is this solving? As far as I know we can't load any other types of workspace file anyway, right?

[msujew]

@tsmaeder The reasoning behind this PR isn't to change the workspace file format, but to allow adopters to specifiy their own file extensions. Right now, it's hard coded to be either .theia-workspace or .code-workspace. End-users of adopter IDEs usually don't care that their IDE is built on top of Theia and they expect everything to be branded towards the actual IDE.

See also this question we had on the discourse forum.

[tsmaeder]

Looked through the code and it seems O.K. I'm just wondering whether it would make more sense to model this as "a list of extensions, one of which is the default" instead of "the default extension plus possibly VS Code".

[msujew]

@tsmaeder Thanks for the feedback. I've adapted the PR to include a simple array of workspace file options, with the first one just being the default.

[tsmaeder]

Some people are never satisfied ;-) Just one more suggestion.

[tsmaeder]

Looks good to me now.

[paul-marechal]

I cancelled an old pending review and GH decided to publish it... Don't mind me.