Python bindings: use MLIR operations to define constant values

In the original implementation, constants could be bound to EDSC expressions in
the binder, independently from other MLIR Values.  A rework of EDSC including
early typing provided the functionality to use MLIR's `constant` operation to
define typed constants instead of binding them separately, but only used it for
index types.  The new declarative builder implementation followed by providing
a call for building `constant` operations of index types but nothing more.
Expose similar builders for integers, floats and functions to match the what
binders allow one to use.

PiperOrigin-RevId: 238421508