☂️ Windows support

[varungandhi-src]

Requested by some customers and prospects. Sub-parts:

Build system:

• Support building the indexer on Windows. Right now, grailbio/bazel-toolchain that we're using doesn't support Windows.

Code changes:

• There are certain code paths which are OS-specific, we need to audit/change those.

Releases:

• Automatically publish a release binary for Windows

Feature support:

• Support MSVC-style command-line flags starting with /.
• Automatic resource directory detection needs to correctly determine the standard library on Windows

Documentation:

• Provide more instructions on generating a compilation database, as people may be using other build systems

Testing:

• Testing against compilation databases using clang (- style arguments)
• Testing against compilation databases using clang-cl
• Testing against compilation databases using MSVC

Desired outcome: Using scip-clang on Windows should be as easy as on Linux or macOS.