Restore sdk-perf-jobs.yml to clean state with only MAUI Desktop adds

Reverts the temporary [pr] scaffolding that commented out every other
public job to focus CI runs on the new MAUI Desktop jobs.  The file now
matches dotnet/performance main exactly except for two added blocks:

  - Public MAUI Desktop BenchmarkDotNet benchmarks (win-x64, channel main)
  - Private MAUI Desktop BDN benchmarks (win-x64-viper, channel main)

Internal runs are where coverage parity matters; the public job stays
single-channel to avoid increasing public CI run time and flakiness.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: LoopedBard3