[clang-tidy] Fix check for generic lambda invented template parameters

[clang-tidy] Fix check for generic lambda invented template parameters

clang-tidy previously relied on there being no identifier for a TemplateTypeParmDecl for checking
whether 'decltype(x)' should be inserted, instead of checking whether or not it is implicit.

D65042 added new names for invented generic lambda template parameters, rendering that check incorrect.