mlir/Presburger/MPInt: move into llvm/ADT (#94953)

MPInt is an arbitrary-precision integer library that builds on top of
APInt, and has a fast-path when the number fits within 64 bits. It was
originally written for the Presburger library in MLIR, but seems useful
to the LLVM project in general, independently of the Presburger library
or MLIR. Hence, move it into LLVM/ADT under the name DynamicAPInt.

This patch is part of a project to move the Presburger library into
LLVM.