Fix std.math.cast, std.ChildProcess, tests on Windows and enable Windows in CI

[leecannon]

The length of time ZLS has been unbuildable with zig master has gotten rather long and there has been multiple PRs to fix it each with a different set of patches...

• Update to use std from zig 0.10.0-dev.2431 #493 Doesn't fix every usage of std.ChildProcess and tests are broken
• expected error union type, found 'std.child_process.ChildProcess' #490 Doesn't fix every usage of std.ChildProcess, tests are broken and doesn't fix std.math.cast
• ChildProcess change #485 Tests are broken and doesn't fix std.math.cast
• update for latest zig master branch zig-0.10.0-dev.2017+a0a2ce92c #481 Tests are broken and doesn't fix std.math.cast

The test "Missing return type" is not a good test as the expected result is dependant on the content of zls.json on the host machine, so I have commented it out.

The test "Open file, ask for semantic tokens" uses a file uri that is invalid on windows, I've changed it to the the same file uri as the other tests.

With these changes the tests pass on windows and can be enabled in the CI.

Fixes #491
Fixes #483

[SuperAuguste]

LGTM! Thank you so much Lee!