MSVC & SDK dirs suddenly hidden from compiler.include_dirs

#153 broke the pywin32 builds by incompatibly hiding the MSVC & SDK dirs from compiler_instance.include_dirs - and decent public access at all. Same for libs.

The problem happened at
https://github.com/mhammond/pywin32/blob/fc69a1ecc150a13433a7a71d61bac52a5f3df42b/setup.py#L695
/ https://github.com/mhammond/pywin32/commit/fc69a1e) ( @zooba )
(And further problems would also occur later in _why_cant_build_extension() at least.)

The VC & SDK dirs are needed for inspection in complex projects.
At best in a compatible way again.

#153 uses (hidden) class vars compiler_instance.__class__.include_dirs which though are set only after instance.initialize() .

PR #172 (tested with pywin32) suggests a potential way of solution and tests - see further comments and commit comments there.

Without solution, strange application code / workarounds like this would be required:
https://github.com/mhammond/pywin32/blob/b52884ae5417fd2f857007ae1c74d4f753591d36/setup.py#L688
https://github.com/mhammond/pywin32/pull/1936/commits/b52884ae5417fd2f857007ae1c74d4f753591d36
https://github.com/mhammond/pywin32/pull/1936

Inspect setup.py around line 695 and the later _why_cant_build_extension() path, then review issue #153 and PR #172, including its proposed tests. The change is done when MSVC and SDK include and library directories remain compatibly inspectable and pywin32 builds no longer require workarounds.