Improved Regex syntax highlighting

[TechPizzaDev]

Improves semantic highlighting of regex by utilizing Roslyn data that was previously unused.
This "breaks" themes that only style the regexp token because new specialized token types were added.

[333fred]

Could you add some screenshots to demonstrate what this looks like?

[TechPizzaDev]

Here are some examples within VSCode with default colors from Visual Studio 2019.

VSCode Light:

VS2022 Light:

VSCode Dark:

VS2022 Dark:

[JoeRobich]

@TechnologicalPizza Thanks so much for adding these tokens. I think we are missing two things to make this complete.

1. For the other token types, we maintain entries in the package.json where we map each token type to a textmate scope to aid in theming.

https://github.com/OmniSharp/omnisharp-vscode/blob/675319476db5713da3e45f6879b0eda44b1863a5/package.json#L3664-L3739

2. We also ship semantic enabled Visual Studio 2019 themes that could be updated to better match the VS 2019/2022 regex colors. (see https://github.com/OmniSharp/omnisharp-vscode/tree/master/themes)

If you feel up to working on these two tasks, please let me know. Otherwise, I am happy to take this PR as is.

[TechPizzaDev]

Seems like something interesting I could look at 👀
I'm not really sure what name should go where but I'll investigate a bit first.

[JoeRobich]

I'm not really sure what name should go where but I'll investigate a bit first.

Some are already defined in the themes. Others will have to be a best guess unless you find something definitive.

https://github.com/OmniSharp/omnisharp-vscode/blob/675319476db5713da3e45f6879b0eda44b1863a5/themes/vs2019_light.json#L543-L583

[TechPizzaDev]

With commit cba7893 these are the default colors that were already in vs2019_dark.json🥳

[JoeRobich]

@TechnologicalPizza Sorry I haven't followed up. Were there any required changes to the Light theme?

[TechPizzaDev]

@JoeRobich I don't think so? The images I uploaded were made with stock themes. This PR doesn't change any themes either.
I couldn't really figure out why the Light theme was brighter though. It seemed to use the same color definitions as the Dark theme but it was somehow brightened by VSCode, unless I missed some specific regex stuff in some light theme somewhere.

[JoeRobich]

Thanks @TechnologicalPizza !