[flang] Implement semantic checks for DEALLOCATE statements.

The parser checks for duplicate dealloc-opts and expr
analysis checks that dealloc-opts are the right type.

Original-commit: flang-compiler/f18@1ade7f66177c8d7698b1e9da12904352c520e9d1
Reviewed-on: https://github.com/flang-compiler/f18/pull/401
Tree-same-pre-rewrite: false