[flang][OpenMP] Initial support the lowering of copyin clause

This supports the lowering of copyin clause initially. The pointer,
allocatable, common block, polymorphic varaibles will be supported
later.

This also includes the following changes:

1. Resolve the COPYIN clause and make the entity as host associated.

2. Fix collectSymbolSet by adding one option to control collecting the
   symbol itself or ultimate symbol of it so that it can be used
   explicitly differentiate the host and associated variables in
   host-association.

3. Add one helper function `lookupOneLevelUpSymbol` to differentiate the
   usage of host and associated variables explicitly. The previous
   lowering of firstprivate depends on the order of
   `createHostAssociateVarClone` and `lookupSymbol` of host symbol. With
   this fix, this dependence is removed.

4. Reuse `copyHostAssociateVar` for copying operation of COPYIN clause.

Reviewed By: kiranchandramohan, NimishMishra

Differential Revision: https://reviews.llvm.org/D127468