meta: Implement ext_framebuffer_multisample_blit_scaled extension

Extension enables doing a multisample buffer resolve and buffer
scaling using a single glBlitFrameBuffer() call. Currently, we
have this extension implemented in BLORP which is only used by
SNB and IVB. This patch implements the extension in meta path
which makes it available to Broadwell.

Implementation features:
 - Supports scaled resolves of 2X, 4X and 8X multisample buffers.

 - Avoids unnecessary shader compilations by storing the pre compiled
   shaders for each supported sample count.

 - Uses bilinear filtering for both GL_SCALED_RESOLVE_FASTEST_EXT and
   GL_SCALED_RESOLVE_NICEST_EXT filter options. This is an allowed
   behavior in the extension's spec.

 - I tried doing bicubic filtering for GL_SCALED_RESOLVE_NICEST_EXT
   filter. It made the edges in the image look little smoother but
   the image gets blurred causing no overall quality improvement.
   For now I have dropped the idea of doing different filtering for
   nicest filter.

V2:
 - Minor changes to simplify the fragment shader.
 - Refactor the code to move i965 specific sample_map computation out
   of Meta. We now use ctx->Const.SampleMap{2,4,8}x variables initialized
   by the driver.
 - Use a simple msaa resolve shader for scaled resolves with scaling
   factor = 1.0.

V3:
 - Make changes to create a string out of ctx->Const.SampleMap{2,4,8}x
   variables and use it in fragment shader.

V4:
 - Make changes to use uint8_t type ctx->Const.SampleMap{2,4,8}x
   variables.

Signed-off-by: Anuj Phogat <[email protected]>
Reviewed-by: Jordan Justen <[email protected]>

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