Add IsBinCovered to get covered state of selected bin

[tmeissner]

This commit adds a function to the protected type which can be used to get the coverage state of a selected bin. It returns true if the bin was covered, false if not. It also returns false for illegal & ignore bins.

The use case is when you build a coverage model only to get the functional coverage, but using constrained random instead the "intelligent random" methods of the CoveragePkg. For example verifying components in a heuristic way like FIFOs.

if not(sv_cover.IsBinCovered(7)) then
  -- generate stimulus to cover BIN #7
end if;

With the new IsBinCovered function you can know if your have to hit specific coverage goals like writing into the FIFO when it's full, or reading when it's empty.

Maybe there is a simpler method already implemented in CoveragePkg, but I didn't find it.

[JimLewis]

The pull request was not mergeable, so I manually added this capability and added it to the singleton data structure. It is currently on the dev branch. Apologies that it took so long.