ban type parameters for macros

[jakemac53]

This came up in #1930.

I also removed the changelog section for now, it hasn't been updated consistently and has only one very old entry. Will bring it back once the proposal moves to accepted.

[rrousselGit]

It's a bit tangential to generic parameters but does this limitation imply that macros' annotated element cannot contain generated types?

Like:

@myMacro
int fn(ClassGeneratedByMyMacro param) => 0;

[jakemac53]

It's a bit tangential to generic parameters but does this limitation imply that macros' annotated element cannot contain generated types?

No it does not. The restriction applies only to macro constructor arguments (for which Type is not an allowed parameter type). Type arguments are no different than normal arguments, but this makes it explicit.

The staged approach makes possible the above example.