[flang] Resolve name in PASS and BIND attributes

These are recognized along with other attributes and saved in
`passName_` and `bindName_`. The functions `SetPassNameOn()` and
`SetBindNameOn()` set them in a symbol if they are present.
They are also written to `.mod` files.

Add `MakePlaceholder()` to make symbols for names that otherwise
wouldn't have one. This allows us to assign a symbol to every name
and report errors for those that don't have one. Make use of this
for PASS names, which don't have explicit symbols.

Change `ObjectEntityDetails` and `ProcEntityDetails` to be sub-classes
of `EntityDetails`. They each contain a superset of the information in
`EntityDetails` so this reduces some duplication.

Original-commit: flang-compiler/f18@404c920840880bf63bb3b0984cb0e1213057d619
Reviewed-on: https://github.com/flang-compiler/f18/pull/256
Tree-same-pre-rewrite: false