tools/sort_sources.py: sort C++ source file names in build files.

tools/git/move_source_file.py updates C++ source file names in
build files for you, but it does not sort the updated file names.

With this tool, you can sort C++ source file names in build files
(both GYP and GN files supported) automatically. It's not perfect
but should work reasonably well.

BUG=456014
TEST=Run the tool against some build files. The results are included in the patch.

Review URL: https://codereview.chromium.org/888873003

Cr-Commit-Position: refs/heads/master@{#315517}

• chrome/chrome_browser_chromeos.gypi[diff]
• chromeos/chromeos.gyp[diff]
• google_apis/BUILD.gn[diff]
• google_apis/google_apis.gyp[diff]
• tools/sort-headers.py[diff]
• tools/sort_sources.py[Added - diff]
• tools/yes_no.py[Added - diff]