GLPixelBuffer*: Add componentCount==1 (ALPHA/RED), 'allowRowStride' utilization AWTGLPixelBuffer* -> GLPixelBuffer*

GLPixelBufferProvider:
  - Default*.getAttributes(): Add componentCount==1 (ALPHA/RED), validate values, throw exception if n/a or not supported
  - Add 'allowRowStride' (as for AWTGLPixelBufferProvider)
    - Add default for true and false

GLPixelBuffer:
  - Add 'allowRowStride' (as for AWTGLPixelBuffer)
  - Fix requiresNewBuffer(..):
    - aquire minByteSize if passed one is <= 0
    - validate minByteSize w/ currentByteSize according to allowRowStride.

AWTGLPixelBuffer: 'allowRowStride' impl. moved to GLPixelBuffer.
PNGImage: Bounds check in getPixelRGBA8(..) and setPixelRGBA8(..)