fix(edt): Avoid inverting gray scale images in EDT

Checking the saturation of the images to identify if the image contains
only gray scale colors. To exclude the purely black and purely white
images, we also check the values of the colors.

Bug: 438210124
Bug: 439592926
Test: manually. attach screenshot to the bug
Flag: android.view.accessibility.force_invert_color
Change-Id: I11c7e663dbb9360cb5d86e3ff72014ecb1f4a698