Rename ImageDecoder.setResize

Bug: 76448408
Bug: 73537624
Test: Ib40d65c68a6c709b6456f2145ad8a5557a941494

setResize is two verbs, and "resize" implies we're changing the size of
an existing object. In truth, the method specifies the desired size. So
rename setResize(int, int) to setTargetSize, which clearly specifies the
behavior.

Rename setResize(int sampleSize) to setSampleSize.

Hide getSampledSize, which looks too similar to the newly named
setSampleSize. In addition, b/76448408 suggests hiding it. It isn't
really necessary anyway, since a client can just call setSampleSize - no
need to query and call setTargetSize manually.

Since there is no way for a client to know that a RAW image couldn't be
decoded to the desired size (could previously be done with
getSampledSize), make setSampleSize do the extra scaling. This is a
better API anyway.

Change-Id: I84c29fdc6bdfb999a7f712fdc069304ae9676ba6