[flang] Reconstruct binding tables for fir.dispatch codegen

Binding tables are needed to perform the fir.dispatch code generation.
The binding tables are defined as fir.global from the initial lowering.
This patch adds the ability to reconstruct the binding tables information
and store the procedure name and binding index for later use by the
fir.dispatch code generation.
Tests will come with follow up patch that makes full use of this information.

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D136141