feat: Allow pip-installed Deephaven embedded server to run directly on Windows (no WSL)

[pchambre]

Added handling to convert between slashes needed by the Web UI and backslashes on the local filesystem. Also removed spaces from default paths, since they are tedious on Windows. Removed one unused import. Added detail to exceptions thrown in FilesystemStorageServiceGrpcImp resolveOrThrow in case there are other scenarios not correctly handled by these changes.

To build on Windows a version after 1.2.0 of the GWT Gradle plug-in is needed. Those changes are not included in this PR; so this branch would still need to be built on Linux, or Mac, or maybe under WSL.

I have made a PR to the GWT Gradle plug-in for the needed change to classpath handling to be able to build on Windows.

Also, note that it is not even possible currently to push from Windows, because pre-push hooks for Spotless don't correctly handle Windows file path separators.

FWIW: I made these changes because I want to use Deephaven with a driver that runs under Windows but cannot be run under WSL.

I have verified that these changes successfully build the Deephaven wheels on Windows 11 and OSX Apple Silicon. A wheel installed with these changes allows the Deephaven server to run with start scripts like those shown here: https://deephaven.io/core/docs/getting-started/pip-install/ and also allows saving and loading Notebooks and data files from the Web UI.

[github-actions]

No docs changes detected for 747a65c

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[pchambre]

I have read the CLA Document and I hereby sign the CLA

[niloc132]

Adding Devin, who worked on the config/data/cache dir feature.

Can you edit the title to reflect that this isn't python/pip specific? This should apply equally when running from a tar distribution with just groovy, etc.

[pchambre]

Adding Devin, who worked on the config/data/cache dir feature.

Can you edit the title to reflect that this isn't python/pip specific? This should apply equally when running from a tar distribution with just groovy, etc.

I have no idea about running this from a tar or without Python. This PR is specifically to address the WSL requirement here: https://deephaven.io/core/docs/getting-started/pip-install/

[pchambre]

My PR to update esoco/gwt-gradle-plugin/ to handle long semi-colon separated paths on Windows has been accepted and merged, so 1.2.1 or later should allow DH Core to build on Windows with the addition of envClasspath=true.