* fix(plugins): hand plugins paths in one form on Windows
Plugins got the project root, editor path, provider documents, code action edits, vcs-status roots and find-files results as D:\… while event paths from the UI use /, so Checkstyle could not find the project of a saved file. The host now converts every path it hands to plugins with ipc_path::to_ipc.
* fix(checkstyle): match native Windows report paths
* test(plugins): use workbench IPC paths in host fixtures