media: Add PlayReady key system in media histograms

Previously, PlayReady related EME queries and playbacks reported as
`Unknown` key system in the histograms.

- Added `PlayReady` key system variant to "KeySystem"
- Added `PlayReady.HardwareSecure` variants to
  "KeySystemWithRobustness"

Now the browser reports with `PlayReady.HardwareSecure` for the
following key systems:
- "com.microsoft.playready.recommendation" with "3000" robustness
- "com.microsoft.playready.recommendation.3000"
- Other PlayReady non hardware secure ones will be reported as Unknown.

Tests:
- Tried three different PlayReady playbacks:
  a) "com.microsoft.playready.recommendation.3000": HardwareSecure
  b) "com.microsoft.playready.recommendation" with 3000 robustness:
     HardwareSecure
  c) "com.microsoft.playready.recommendation" with 2000 robustness:
     Unknown
- Captured histograms (chrome://histograms/#playready): See
  http://shortn/_2m2Pyw1C4a

Bug: 378869813
Change-Id: I31ddc89d80e31a2b59a0d4153410c02b9a3a88b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6404530
Commit-Queue: Sangbaek Park <sangbaekpark@chromium.org>
Reviewed-by: Evan Liu <evliu@google.com>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Vikram Pasupathy <vpasupathy@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1444961}