Set "binary_size_plugin" output.property on Build-Stats-* bots

* The output.property looks like this: {"canvaskit.wasm": 7394679}
  (from https://ci.chromium.org/raw/build/logs.chromium.org/skia/5236eb95c4490b11/+/annotations)

* Refactored scripts to avoid hardcoding the magic_seperator and total_size_bytes.

* Added this capability to all 4 infra/bots/buildstats/* scripts.

* Added missing tests for analyze_web_file and analyze_cpp_lib.


The output.property will be eventually consumed by a Gerrit plugin to display change in bytes in the UI.

Note: buildstats_cpp.py is not currently used by any bot. But if it is in the future it will work.

No-Tree-Checks: true
Bug: skia:11744
Change-Id: I593bae8ff73c35089cc2785a1cc4bc5b630007c4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377840
Commit-Queue: Ravi Mistry <rmistry@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
8 files changed