Set presubmit line length check to 100 for Rust

Rust style dictates 100 columns instead of 80. Update presubmit check
accordingly.

Bug: chromium:1292073
Change-Id: I4f0c0cc3b84ebb4559f29a6500ffd843febc8f93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4295201
Auto-Submit: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

presubmit_canned_checks.py

@@ -520,6 +520,7 @@ def CheckLongLines(input_api, output_api, maxlen, source_file_filter=None):
       'java': 100,
       # This is specifically for Android's handwritten makefiles (Android.mk).
       'mk': 200,
+      'rs': 100,
       '': maxlen,
   }