fortran: ASSOCIATE with contained-function selector rejecting type-bound calls

Two issues prevented ASSOCIATE constructs whose selector is a call to a
contained function from subsequently calling type-bound procedures on the
associate name.

When the selector is a contained function, resolving it
at parse time (before CONTAINS is fully processed) prematurely set the
function's attribute to FL_PROCEDURE/EXTERNAL, conflicting with its later
declaration as an internal procedure and giving a spurious "attribute
conflict" error.

When the first access is a generic type-bound procedure name, no candidate
type was found, and the associate name got no type, giving "no IMPLICIT type".
Now also search type-bound procedure names via gfc_find_typebound_proc; exclude vtable
types to avoid false positives.

Assisted by: Claude Sonnet 4.6

	PR fortran/125530

gcc/fortran/ChangeLog:

	* match.cc (gfc_match_call): Route ASSOCIATE names followed by '%'
	to match_typebound_call without first resolving the selector, to
	avoid prematurely marking a contained-function selector as EXTERNAL.
	* symbol.cc (find_derived_types): Also search type-bound procedure
	names via gfc_find_typebound_proc when inferring the type of an
	inferred-type ASSOCIATE name; exclude vtable types.

gcc/testsuite/ChangeLog:

	* gfortran.dg/associate_contained_func_typebound.f90: New test.
	* gfortran.dg/associate_contained_func_typebound_2.f90: New
	run-time test exercising generic resolution and a module-scope
	selector.

(cherry picked from commit 64fee7f4475c756fc17fa9e15aee7683e716ba8a)