fix Issue 12967 - Prefix method 'this' qualifiers should be disallowed in DeclDefs scope
Check redundant/conflicting attributes between prefix and postfix
Fix another broken case of qualified anchors.

The previous fix didn't work for template members of templated structs.
Update ddoc test to expect fully-qualified symbols.
Fixup

Remove redundant braces.
Merge pull request #3689 from 9rnsr/fix12967

Issue 12967 - Prefix method 'this' qualifiers should be disallowed in DeclDefs scope
Merge pull request #3695 from quickfur/more_ddoc_anchors

DDOC fully-qualified anchors for template members of template structs/classes