[flang] Semantics for SELECT TYPE

    Summary:
    Added support for all semantic checks except C1157
    was previously implemented.

    Address review comments.

    Reviewers: PeteSteinfeld, tskeith, klausler, DavidTruby, kiranktp, anchu-rajendran, sscalpone

    Subscribers: kiranchandramohan, llvm-commits, flang-commits

    Tags: #llvm, #flang

    Differential Revision: https://reviews.llvm.org/D79851