Support BEF on Windows machines

[plaird]

As a BEF user
I would like to use Eclipse+BEF on my Windows machine
Such that all the features work as expected

Background:
I am filing this having only tested on Mac and Linux. I assume the BEF will need to be updated to support Windows (path constructions, etc) but I don't know the scope of work right now. I will need to get a Windows machine to do the assessment.

[plaird]

Doc note about Windows now included in install.md

https://github.com/salesforce/bazel-eclipse/blob/master/docs/install.md#supported-platforms

[plaird]

I have made a lot of progress on this, and the tests are almost passing now. I expect to be done with this soon.

[plaird]

MVP support on Windows is now done. Remaining work:

• Problems View is not showing some errors. I need to compare the behavior of the Problems view before and after current state and 1.3.0. I believe there is a regression there, but not sure yet.
• Figure out why 3 Problems tests are failing on Windows but not Mac
• Test launchers need more testing on Windows. see Issue Fix test launcher for Bazel JUnit tests #251
• Set a better default value for the Bazel Preference for the path to Bazel Executable for Windows.
• Dedicated Windows install/user guide documentation supplement.
• Centralize the "\\" regex pattern
• Test this whole thing on Linux, to make sure we are still good there
• Test install BEF into Windows Eclipse via update site and archive zip
• Add a Windows job to GitHub Actions PR build in CI

I probably won't get to this next task in this work item, if not file as a follow up issue:

• Most of this porting work was distinguishing String paths between Bazel and Filesystem paths. On *nix, the delimiter is the same so we could be vague and it worked. But to prevent Windows bugs from being introduced into the code we need to strongly type any variable that is holding a path. Something like BazelLabel (already have this) and BazelFilesystemPath (relative paths in the workspace but in FS delimiter form). (Filed as an issue in bazel-java-sdk)

[plaird]

All the remaining action items have been resolved. Closing....we now officially support Windows.