Fix encoding of runfiles manifest and repository mapping files.

See bazelbuild/bazel#374 (comment):

> all output files produced by Bazel should use UTF-8 and \n line endings on
> all platforms, including Windows.

Author: phst

CHANGELOG.md

@@ -59,6 +59,8 @@ Unreleased changes template.
 * (gazelle) Providing multiple input requirements files to `gazelle_python_manifest` now works correctly.
 * (pypi) Handle trailing slashes in pip index URLs in environment variables,
   fixes [#2554](https://github.com/bazelbuild/rules_python/issues/2554).
+* (runfiles) Runfile manifest and repository mapping files are now interpreted
+  as UTF-8 on all platforms.
 
 {#v0-0-0-added}
 ### Added

python/runfiles/runfiles.py

@@ -56,7 +56,7 @@ def RlocationChecked(self, path: str) -> Optional[str]:
     def _LoadRunfiles(path: str) -> Dict[str, str]:
         """Loads the runfiles manifest."""
         result = {}
-        with open(path, "r") as f:
+        with open(path, "r", encoding="utf-8", newline="\n") as f:
             for line in f:
                 line = line.rstrip("\n")
                 if line.startswith(" "):
@@ -367,7 +367,7 @@ def _ParseRepoMapping(repo_mapping_path: Optional[str]) -> Dict[Tuple[str, str],
     if not repo_mapping_path:
         return {}
     try:
-        with open(repo_mapping_path, "r") as f:
+        with open(repo_mapping_path, "r", encoding="utf-8", newline="\n") as f:
             content = f.read()
     except FileNotFoundError:
         return {}