Default all new bitmaps to sRGB colorspace unless explicitly requested.

This fixes breakages in the WideColorGamutTests that resulted from a
change in Skia. Skia now treats all non-tagged sources as sRGB instead
of sometimes assuming sRGB_linear.

Test: atest CtsUiRenderingTestCases
Bug: 111836790
Change-Id: If7b1c00ad889446658f98e9ad644869e2eeabcdb