find-msvc-tools: consider adding a public function to find Windows SDK tools

[lambdageek]

I would like to be able to find the Windows resource compiler rc.exe which is in the Windows SDK bin dir, not in the MSVC tools bin dir.

Currently, I'm doing a hack https://github.com/rust-lang/rust/pull/146018/files#diff-8a40df8ee7be3d238589677ae282637037040cceca3dc167c3e234db981245cfR137 - using find_tool and then looking at the PATH to get the ucrt bin directory. It would be nicer if get_ucrt_dir was public.

Context: rust-lang/rust#146018

[NobodyXu]

Released find-msvc-tools v0.1.1 with the function set as public