Move canonicalize_path tests into separate file

canonicalize_path has a lot of tests. Move these tests into its own .cpp
file to avoid cluttering test-file.cpp.

This commit should not change test coverage.

Author: strager

test/CMakeLists.txt

@@ -40,6 +40,7 @@ quick_lint_js_add_executable(
   test-error-formatter.cpp
   test-error-list.cpp
   test-error.cpp
+  test-file-canonical.cpp
   test-file-path.cpp
   test-file.cpp
   test-gmo.cpp