[Dexter] Add support for Windows to regression test suite.

[Dexter] Add support for Windows to regression test suite.

This patch addresses the issue of the regression suite not running on windows
hardware. It changes the following things:

* add new dexter regression suite command to lit.cfg.py that makes use of the
  clang-cl_vs2015 and dbgend builder and debuggers.

* sprinkle the new regressionsuite command through the feature and tool tests
  that require them.

* mark certain problem tests on windows

* [revert fix] fixed darwin regression test failures by adding unsupported line
  for system-darwin to command tests.

There's a couple of tests that fail (or pass) in unexpected ways on Windows.

Problem tests are both the penalty and perfect expect_watch_type.cpp tests.
Type information reporting parity is not possible a this time in dexter due to
the nature of how different debuggers report type information back to their users.

reviewers: Orlando

Differential Revision: https://reviews.llvm.org/D76609