VideoTrackRecorder: Refactor the encoder look up code

This CL refactors the code of looking up available encoder and profile
for a given codec id in VideoTrackRecorder. After the CL, the software
available encoder logic is in a single place.

Bug: 331628586
Test: blink_unttests

Change-Id: I564598a91c43b7424a3a979834027d8342a8ec81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5409791


Reviewed-by: Markus Handell <handellm@google.com>
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282312}