[vscode] Syntax highlighting for Coq 8.17-8.20

[4ever2]

Add updated syntax from VSCoq Legacy and extend with new commands from Coq 8.17-8.20

[Alizter]

Did you cover the list in #854? I haven't been able to fully check myself yet.

[4ever2]

Not all of them are covered by this PR. Some of them seem quite hard to fix.
I don't think there is a good way to fix highlighting on Set and Add other than adding all the possible settings to the grammar.

[Alizter]

I guess to do Set correctly you will have to look at all the options. IIRC there should be a vernac command that prints the options table, so that might be a way to start on such a list.

I can't tell if Register some_constant. will get highlighted, I can see Register Scheme is picked up.

Also, I can't tell if Add Search Blacklist is also considered.

I've updated the list accordingly since presumably we will merge this anyway.

[4ever2]

Register some_constant. will highlight Register as a command but not some_constant as an ident.
Add Search Blacklist is not considered here.

[Alizter]

Register some_constant. will highlight Register as a command but not some_constant as an ident.

That's fine, as long as Register is being picked up.

[ejgallego]

That's fantastic, thanks so much @4ever2 !