Crash on windows

Resolving classpath fails on Windows on the following line https://github.com/fwcd/kotlin-language-server/blob/80fc538635beff0b36ade6f955cd7b552c5e3a9f/shared/src/main/resources/projectClassPathFinder.gradle#L24

With the error `character to be escaped is missing`

This can be traced to the `File.separator` being `\` on Windows.

I'm not very familiar with Java strings, but I was able to resolve the issue by hardcoding `\\\\` (!) instead of `File.separator`

Start in shared/src/main/resources/projectClassPathFinder.gradle at line 24 and inspect how File.separator is used in the classpath resolution. Reproduce the Windows error "character to be escaped is missing" and verify that classpath resolution completes successfully on Windows without relying on an incorrect separator escape.

Written by the indexing model from the issue text.