mesa: Fix querying location of nth element of an array variable

mesa: Fix querying location of nth element of an array variable

This patch makes changes to the behavior of glGetAttribLocation(),
glGetFragDataLocation() and glGetFragDataIndex() functions.

Code changes handle a case described in following example:

shader program:
layout(location = 1)in vec4[4] a;
void main()
{
}

Currently, glGetAttribLocation("a") returns 1.
glGetAttribLocation("a[i]"), where i = {0, 1, 2, 3}, returns -1.
But the expected locations for array elements are: 1, 2, 3 and 4
respectively.

This clarification came up with the addition of
ARB_program_interface_query to OpenGL 4.3.

From Page 326 (page 347 of the PDF) of OpenGL 4.3 spec:
   "Otherwise, the command is equivalent to

    GetProgramResourceLocation(program, PROGRAM_INPUT, name);"

And, From Page 101 (page 122 of the PDF) of OpenGL 4.3 spec:

   "A string provided to GetProgramResourceLocation or
    GetProgramResourceLocationIndex is considered to match an active
    variable if

    • the string exactly matches the name of the active variable;
    • if the string identifies the base name of an active array, where
      the string would exactly match the name of the variable if the
      suffix "[0]" were appended to the string; or
    • if the string identifies an active element of the array, where
      the string ends with the concatenation of the "[" character, an
      integer (with no "+" sign, extra leading zeroes, or whitespace)
      identifying an array element, and the "]" character, the integer
      is less than the number of active elements of the array variable,
      and where the string would exactly match the enumerated name of
      the array if the decimal integer were replaced with zero."

V2: Simplify get_matching_index() function.
    Add relevant text from OpenGL spec in commit message.

Fixes failures in Khronos OpenGL CTS tests:
explicit_attrib_location_room
draw_instanced_max_vertex_attribs

Proprietary linux drivers of NVIDIA (331.49) matches the behavior
expected by OpenGL 4.3 spec.

Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>