c++: consteval-defarg1.C test variant for templates

c++: consteval-defarg1.C test variant for templates

We weren't recognizing a default argument for a consteval member function as
being in immediate function context because there was no function parameter
scope to look at.

The following testcase is an attempt to test it with templates, both
non-dependent and dependent consteval calls in both function and class
templates, and with r11-5694 it now passes.

2020-12-03  Jakub Jelinek  <jakub@redhat.com>

	* g++.dg/cpp2a/consteval-defarg2.C: New test.