Fixes #178

The root cause is vite always passes in a path with upper case drive letter for importer, but vite.normalizePath does not change the drive letter casing, so when invoked from working directory with lower case drive letter, the config dir is lower case and the importer is upper case, and it will fail to compute a relative path from config dir to importer

In the previous fix, the paths are normalized to lower case, but vite still passes in upper case drive letter for importer and the previous fix didn't call fixFilePathCasing on the importer. So no paths could ever get resolved on Windows (since importer is always upper and configDir always lower case)

I'm fixing this using a simpler approach by only changing path.normalize to capitalize the drive letter. This way, the change is a no-op for non-Windows and for people always using upper case drive letters, which should be much lower risk.

I looked at the is-fs-case-sensitive package and it uses a really dirty hack IMO, which doesn't even cover all the cases since Windows can have per-directory filesystem case sensitivity. So IMO it's better to only change the drive letter part, which should be always case insensitive

Testing
Tested on a minimal project on my Windows environment and the environment I initially discovered this in (which uses lower case drive letter by default)
Verified running build succeeds with both upper and lower case drive letter as working directory