Allow more specific theme modifications with semantic highlighting enabled

[dibarbet]

Original context - dotnet/csharp-tmLanguage#266 (comment)

With textmate, it is possible to have very specific configurations for highlighting, for example you can configure it to highlight the 'event' keyword differently from the 'class' keyword because it has separate scopes for each (though both under the keyword scope).

With semantic highlighting, these all end up under the 'plainKeyword' scope so you cannot differentiate.

This tracks the request to have semantic highlighting be able to differentiate between these, potentially with modifiers.

[wise0704]

This is worse now as of version 2.0.320.

plainKeyword has been changed to just keyword, which has a hardcoded textmate scope of keyword.control:
https://github.com/microsoft/vscode/blob/2ccd690cbff1569e4a83d7c43d45101f817401dc/src/vs/platform/theme/common/tokenClassificationRegistry.ts#L545C2-L545C2

And on top of that, this extension adds another scope keyword.cs on top of that:

vscode-csharp/package.json

Lines 4771 to 4773 in 68d5768

	"keyword": [
	"keyword.cs"
	],

Previously with plainKeyword = [ keyword.cs ], avoiding having only a single colour for every keyword was possible by not setting anything for keyword textmate scope in theme.

Now that's not possible, because keyword = [ keyword.cs, keyword.control ] and it's impossible to not assign keyword.control to a colour.

It really needs to roll back to plainKeyword (because now we can't even differentiate between control keywords and every other keyword), and then personally I would prefer plainKeyword to not have any textmate fallbacks assigned - many other languages do this, since detecting keyword is most of the time possible with textmate, and use semantic highlighting to mainly focus on entity identification (class, variables, non-invocation methods, constants, etc.) which is impossible to detect with textmate.