[mlir] Add option to disable MLIR Python dev package configuration. (#117934)

Adds a CMake option MLIR_DISABLE_CONFIGURE_PYTHON_DEV_PACKAGES which
gates doing package discovery and configuration for Python dev packages
by MLIR (this was made opt-out to preserve compatibility with
find_package(MLIR) based uses which do not set the standard options).

The default Python setup that MLIR does has been a problem for
super-projects that include LLVM for a long time because it forces a
very specific package discovery mechanism that is not uniform in all
uses.

When reviewing #117922, I noted that this would effectively be a break
the world event for downstreams, forcing them to adapt their nanobind
dep to the exact way that MLIR does it. Adding the option to just
wholesale skip the built-in configuration heuristics at least gives us a
mechanism to tell downstreams to migrate to, giving them complete
control and not requiring packaging workarounds. This seemed a better
option than (once again) creating a situation where downstreams could
not integrate the dep change without doing tricky infra upgrades, and it
removes the burden from the author of that patch from needing to think
about how this affects super-projects that include MLIR (i.e. they can
just be told to do it themselves as needed vs being in a wedged state
and unable to upgrade).

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