Update Configuration#isScreenWideColorGamut doc

Clarify that the method does not imply the screen is color-managed.
A global color transform may still be applied depending on the user
settings, such as night light, accessibility, Boosted, or Stretched.

Bug: 78012876
Test: builds
Change-Id: Ie9cdf455cf4ca93be2357a5313cd63555ab91ff9