[flang] Add getTypeDescriptorBindingTableName function

Type descriptor and its binding table are defined as fir.global in FIR.
Their names are derived from the derived-type name. This patch adds a new
function `getTypeDescriptorBindingTableName` in the NameUniquer and
refactor the `GetTypeDescriptorName` function to reuse the same code.
This will be used in the fir.dispatch code generation.

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D136167