[flang] More derived type name resolution

Track PRIVATE statement in derived type components and in procedure
bindings. These are recorded in derivedTypeInfo_ (along with the name
appearing in EXTENDS) and used to modify the accessibility attributes of
components and bindings. Also track SEQUENCE statement.

Detect erroneous PRIVATE in derived types that aren't in modules.
Detect incompatible SEQUENCE types.

Save EXTENDS symbol and SEQUENCE in DerivedTypeDetails and write them to
the .mod file.

Original-commit: flang-compiler/f18@f29d6207140bb818442b2d5cb7de067a34082b61
Reviewed-on: https://github.com/flang-compiler/f18/pull/175
Tree-same-pre-rewrite: false