When validating format+type+internalFormat for texture pixel operations
on GLES3, the effective internal format should be used if the one
specified is an unsized internal format. Page 127, section "3.8 Texturing"
of the GLES 3.0.4 spec says:

    "if internalformat is a base internal format, the effective internal
     format is a sized internal format that is derived from the format and
     type for internal use by the GL. Table 3.12 specifies the mapping of
     format and type to effective internal formats. The effective internal
     format is used by the GL for purposes such as texture completeness or
     type checks for CopyTex* commands. In these cases, the GL is required
     to operate as if the effective internal format was used as the
     internalformat when specifying the texture data."

v2: Per the spec, Luminance8Alpha8, Luminance8 and Alpha8 should not be
considered sized internal formats. Return the corresponding unsize format
instead.

v4: * Improved comments in
      _mesa_es3_effective_internal_format_for_format_and_type().
    * Splitted patch to separate chunk about reordering of
      error_check_subtexture_dimensions() error check, which is not directly
      related with this patch.
v5: Dropped the splitted patch because it was actually a work around 3
    dEQP tests that are buggy:

    dEQP-GLES2.functional.negative_api.texture.texsubimage2d_neg_offset
    dEQP-GLES2.functional.negative_api.texture.texsubimage2d_offset_allowed
    dEQP-GLES2.functional.negative_api.texture.texsubimage2d_neg_wdt_hgt

Cc: "11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>