[flang][NFC] Simplify mapSymbolAttributes in symbol lowering

mapSymbolAttributes currently has a lot of very similar code for
each kind of explicit shape and scalar symbols.

Refactor it so that the change to lower symbols with fir.declare
can be added in centralized places instead of being scattered.
This is a preparation patch and fir.declare is not yet added.

Differential Revision: https://reviews.llvm.org/D136061