Inlay hints for 1-occurrence only macro_rules

Minimization/specialization of #11323: Please show inlay hints for invocations of macro_rules!-based macros, where the active/applied rule/part of that macro_rules! uses/outputs the relevant captured macro $variable ONCE ONLY. (That is, the relevant capturing $variable is not used in any active/applied part's $(...)+ or $(...)*, and it's not used/printed twice or more in the active/applied branch of the macro_rules!.)

This may sound useless or too restrictive. BUT, macro designers can design a rust-analyzer-only feature that would have such dummy macros (selected by conditional compilation based on the feature's presence). That would be used with rust-analyzer only - not to be used for debug/production. (These dummy macros could be much simpler than the real debug/release macros, simplified by potentially using unreachable!() or unreachable!() as XXX to generate any missing/complex values. When under that feature, the crate can also conditionally import no-link crate to ensure that it can't be linked to.)

Then debug/production builds would use the real macro_rules! implementation (or have a macro_rules! shim that forwards to a (separate) proc macro crate instead, or just pub use re-export the proc macros from a (separate) proc macro crate). That doesn't need to have any inlays shown.

(For proc macros that would mean addition of another, non-proc macro, crate, which either forwards the requests or re-exports the proc macros for debug/release builds and switches to the dummy macro_rules! when under a feature dedicated to rust-analyzer. But this refactoring is trivial. And the proc macros may already be forwarded/re-exported from a user-facing non-proc-macro crate anyway.)

The issue names no file or test; start by tracing rust-analyzer's existing inlay-hint handling for macro_rules! invocations. Establish how the active rule and captured variables are identified, then verify completion against the one-occurrence restriction, including repeated uses and captures in + or * repetitions.