Add `@phan-real-param` annotation option?

When that annotation is used, pretend it is the real signature type for analysis purposes. Warn if they are incompatible or about not being fully supported if they overridden by other methods

This can be used to generate stubs with the equivalent of union types, or newer features, or resource.
(e.g. to prepare for upgrading an extension or php version, in combination with internal stubs)

This may be useful for tooling that removes syntax incompatible with older php versions.

Phan already supports @phan-real-return

/** @phan-real-param array|int $x */
function test($x) {
     
}
test('test');  // Should emit stricter real type mismatch warning

Start by locating Phan's existing @phan-real-return support and tracing how annotations affect signature analysis. Define the behavior for @phan-real-param, including incompatible calls and overrides, then add coverage for the union-type example and verify the intended warnings.