[ASTImporter] Import the default argument of TemplateTypeParmDecl

The test case isn't using the AST matchers for all checks as there doesn't seem to be support for
matching TemplateTypeParmDecl default arguments. Otherwise this is simply importing the
default arguments.

Also updates several LLDB tests that now as intended omit the default template
arguments of several std templates.

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D92103