_mesa_create_exec_table: GLES3 fixes.

_mesa_create_exec_table: GLES3 fixes.

This patch sets up the dispatch table for the following GLES3
functions when a GLES3 context is in use:

- BeginQuery
- BeginTransformFeedback
- BindSampler
- BindTransformFeedback
- BlitFramebuffer
- ClearBufferfi
- ClearBufferfv
- ClearBufferiv
- ClearBufferuiv
- ClientWaitSync
- CopyBufferSubData
- DeleteQueries
- DeleteSamplers
- DeleteSync
- DeleteTransformFeedbacks
- EndQuery
- EndTransformFeedback
- FenceSync
- FramebufferTextureLayer
- GenQueries
- GenSamplers
- GenTransformFeedbacks
- GetInteger64v
- GetQueryObjectuiv
- GetQueryiv
- GetSamplerParameterfv
- GetSamplerParameteriv
- GetStringi
- GetSynciv
- GetTransformFeedbackVarying
- GetVertexAttribIiv
- GetVertexAttribIuiv
- IsQuery
- IsSampler
- IsSync
- IsTransformFeedback
- PauseTransformFeedback
- RenderbufferStorageMultisample
- ResumeTransformFeedback
- SamplerParameterf
- SamplerParameterfv
- SamplerParameteri
- SamplerParameteriv
- TransformFeedbackVaryings
- VertexAttribDivisor
- VertexAttribIPointer
- WaitSync

And it avoids setting up the dispatch table for these non-GLES3
functions:

- ColorMaski
- GetBooleani_v
- Enablei
- Disablei
- IsEnabledi
- ClearColorIiEXT
- ClearColorIuiEXT
- TextureStorage2DEXT
- TextureStorage3DEXT
- GetActiveUniformName
- GetnUniformdv
- GetnUniformfv
- GetnUniformiv
- GetnUniformuiv

Reviewed-by: Brian Paul <brianp@vmware.com>
v2: Make the ctx argument to _mesa_init_transform_feedback_dispatch()
a const pointer.  Add a comment to remind us to add
GetBufferParameteri64v once tests exist for it.  Also add
VertexAttribDivisor for GLES3, and remove GetActiveUniformName and
GetnUniform{dv,fv,iv,uiv} for GLES3.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>