[flang] Change when symbol is set in parser::Name

Rework how `parser::Name` is resolved to contain a `Symbol`. so that
constants in types can be evaluated. For example:
```
  integer, parameter :: k = 8
  integer(k) :: i
```
The old approach of collecting the symbols at the end of name resolution
and filling in the `parser::Name` does not work because the type of `i`
needs to be set in the symbol table.

The symbol field in `parser::Name` is now mutable so that we can set it
during name resolution. `RewriteParseTree` no longer needs to do that
(it still warns about unresolved ones), so it does not need to collect
symbols and fill them in. Consequently, we can eliminate "occurrences"
from symbols -- we just need the name where each is first defined.

This requires a lot of refactoring in `resolve-names.cc` to pass around
`parser::Name` rather than `SourceName` so that we can resolve the
name to a symbol.

Fix some bugs where we stored `SourceName *` instead of `SourceName`
in the symbol table. The pointers were into the parse tree, so they
were only valid as long as the parse tree was around. The symbol
table needs to remain valid longer than that, so the names need to
be copied. `parser::Name` is not used in the symbol table.

Eliminate `GenericSpec`. Currently all we need to do is to resolve
the kinds of GenericSpec that contain names.

Add `ScopeName` kind of `MiscDetails` for when we need a symbol in
the scope to match the name of the scope. For example, `module m`
cannot contain a declaration of a new `m`. Subprograms need real
details because they can be called recursively.

Fix output of partially resolved modules where we know it is a submodule
but have not yet resolved the ancestor.

Original-commit: flang-compiler/f18@5c1a4b99d2421f5b32e83426488d3fdf7951cfba
Reviewed-on: https://github.com/flang-compiler/f18/pull/238
Tree-same-pre-rewrite: false