Add semantic token type 'constructor'

[0dinD]

This PR adds a more specific token type for constructors, called constructor, which will allow constructors to be colored differently from methods, if desired. I could submit a PR to vscode-java, similar to redhat-developer/vscode-java#1540, which would allow method to be the supertype of constructor, in order to avoid breaking current color themes.

Unfortunately, I encountered a problem whilst implementing this: when a VS Code client receives a constructor token, the semantic highlighting completely breaks for that file. After some debugging, I found out that it was a bug in VS Code, so I have submitted an issue (microsoft/vscode#103104) about that. Until that gets fixed, this PR is not ready to be merged.

[0dinD]

microsoft/vscode#103104 has been fixed in VS Code Insiders now, and will probably release in VS Code 1.49, at which point this PR would be ready to merge as long as vscode-java declares 1.49 as the minimum version.

But while working on #1539, I realized that we could also provide the same feature by adding a constructor modifier and making the token type of constructors class, interface, enum etc instead of function.

This would give even more flexibility in styling constructors than a constructor token type. For example, you could choose between styling them exactly like their respective types or styling them like methods, with a selector like *.constructor.

The only downside that I can see is that we change the token type of constructors from function to class, interface, enum etc, which would break color themes that don't update to also specify *.constructor.

@fbricon what do you think? Should constructor be a token type or a modifier to class, interface, enum etc?

[0dinD]

Closing after discussion with Eskibear.