Compiling Kotlin on Windows appears to require `--legacy_external_runfiles`

[smowton]

Bazel version: 8.1.1
rules_kotlin version: 2.1.3

I found that Kotlin compilation jobs specifically on Windows would fail with an Rlocation error complaining that the jars required to run the Kotlin compiler weren't in the manifest:

---8<---8<--- Start of log, file at C:/tmp/bazel-workers/worker-3-KotlinCompile.log ---8<---8<---
LAUNCHER ERROR: Rlocation failed on _main/external/rules_kotlin++rules_kotlin_extensions+com_github_jetbrains_kotlin_git/lib/annotations-13.0.jar, path doesn't exist in MANIFEST file
---8<---8<--- End of log ---8<---8<---

Noting that this began _main/external, and the actual manifest written to disk to run build.exe did contain annotations-13.0.jar but didn't have that _main/external prefix, I tried adding build:windows --legacy_external_runfiles to my bazelrc and the build now succeeds.

Note that our repository separator has been set to + rather than ~ in the example above; this appears consistently in the requested path and the manifest, so does not appear related to this issue.

Possibly relevant: my build already has build:windows --enable_runfiles for unrelated reasons.