Add coverage test case for generated struct methods
The body of implicitly generated opAssign should not appear in coverage result.
The body of implicitly generated __cpctor should not appear in coverage result.
The body of implicitly generated __(aggr|field)Postblit should not appear in coverage result.
The body of implicitly generated __(aggr|field)Dtor should not appear in coverage result.
Merge pull request #2021 from 9rnsr/fix_loc

Fix coverage output for generated aggregate methods.