Consider reserving keywords for upcoming features

[markcowl]

All those reservations needs to  only prevent declaration names to use them, property, variant and enum member names should all be allowed to use those.

Potential keywords:

• flag (For a flag enum, I think it might be quite beneficial for doing built in things like Foo.a | Foo.b)
• data We talked many times about having data decorators(auto set and provide read accessor for the input)
• state We talked about the possibility to define state engine in TypeSpec
• partial Partial models
• macro Macros
• private Mark types as private
• local Mark types/const as local/private
• keyof Similar to typescript
• package Some package declaration
• metadata Metadata registration
• env define environment(Retrieve value from environemnt variable)
• arg similar but with some Cli arguments
• declare Keyword for making a declaration of an expression(unification of expression and declaration)
• sealed Explicitly seal a model
• array if we ever wanted to try to detach arrays from models
• struct similar to above

If we add back some logic into the language(if else will remain reserved after projection removal)

• switch
• case
• match

[chrisradek]

We also talked about sealed as a potential keyword to explicitly say nothing new can be added - even when extending a sealed model.