Add per-feature logging for OnDeviceModel.Android.GenerateResult.

This change introduces a new parameterized histogram
`OnDeviceModel.Android.GenerateResult{ModelExecutionFeature}` to track
the results of generate requests on Android, broken down by the specific
model execution feature. The existing
`OnDeviceModel.Android.GenerateResult` will continue to log for all
features.

The initial version was generated by Cider Agent with the following
prompt:

Help me add a new histogram below "OnDeviceModel.Android.GenerateResult"
that has a suffix of ModelExecutionFeature. For example,
"OnDeviceModel.Android.GenerateResult.ScamDetection". You can use the
helper function in optimization_guide_util but remember to add it to the
BUILD.gn file. Update the histograms.xml file too. For now, you can
assume that the only possible suffix is
MODEL_EXECUTION_FEATURE_SCAM_DETECTION.

Bug: 425408635
Change-Id: Ic350a3585cda0e7f07f7f774992031d9c07b88a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6867814
Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Xinghui Lu <xinghuilu@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1504312}