Updated Bitmap mutablity documentation and removed Bitmap#mIsMutable

flag

Updated Bitmap java and native implementation to redirect queries of
mutability to the native implementation provided by Skia. Updated
documentation of Bitmap.createBitmap method to accurately describe
mutability of the Bitmap result based on various inputs.
Removed flag from Bitmap class in favor of querying jni API directly.
Updated Bitmap constructor to no longer utilize mutable parameter
provided by jni call. Created hidden setImmutable method that invokes
corresponding native method to flip the Bitmap's mutability flag.

Fixes: 65560449
Test: Re-ran CTS tests and updated Bitmap tests to verify mutability of
all creation methods

Change-Id: I1b0b9de2fc15369b4e3f83512b866915387ac926