Createdump fixes and cleanup. (dotnet/coreclr#11368)

Createdump fixes and cleanup. (dotnet/coreclr#11368)

Fixed "with heap" option to actually include all the heaps. The way /proc/$pid/maps
was parsed missed most of the RW data/heap regions.

Added -u/--full full core dump options.

Removed the useless m_memStatus variable in enummem.cpp.

Commit migrated from https://github.com/dotnet/coreclr/commit/3fb9d8d2fe094f09a914d31a551e14fe8a1f2215