Fix Debug Failure crash when resolving overloaded decorators with explicit tuple rest parameters

[hayatexe]

Fixes #63094

Description
When utilizing --experimentalDecorators on methods or accessors, the compiler crashed with a Debug Failure. False expression. at getArgumentArityError if a decorator had an explicitly typed tuple rest parameter (e.g. ...args: [any, any, any]) and an overload match failed.

This happened because getLegacyDecoratorArgumentCount incorrectly evaluated signature.parameters.length instead of getParameterCount(signature) when deciding whether the decorator expects 2 or 3 parameters. Since the node length of a rest parameter is 1 (e.g., ...args), the function erroneously returned 2, which bypassed some argument arity checks and later dropped into getArgumentArityError with args.length = 3 and max = 3. This triggered a crash trying to get first() on args.slice(3).

This PR fixes the crash by using getParameterCount(signature) within getLegacyDecoratorArgumentCount to appropriately count effective parameters over rest arguments.

A compiler test is included.

[Andarist]

There is already an open PR fixing this: #63098