c++: Dependent conversion operator in concept [PR94597]

c++: Dependent conversion operator in concept [PR94597]

When building the parameter mapping for an atomic constraint,
find_template_parameters does not spot the template parameter within the
conversion-type-id of a dependent conversion operator, which later leads to an
ICE during substitution when looking up the missing template argument for this
unnoticed template parameter.

gcc/cp/ChangeLog:

	PR c++/94597
	* pt.c (any_template_parm_r) <case IDENTIFIER_NODE>: New case.  If this
	is a conversion operator, visit its TREE_TYPE.

gcc/testsuite/ChangeLog:

	PR c++/94597
	* g++.dg/cpp2a/concepts-conv2.C: New test.