mesa/shaderapi: Fix TRANSFORM_FEEDBACK_VARYING program query

mesa/shaderapi: Fix TRANSFORM_FEEDBACK_VARYING program query

Fixes the program queries API (glGetProgramiv):
TRANSFORM_FEEDBACK_VARYINGS and TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH
in two cases:

  1. ARB_enhaced_layouts:

The queries were not working for GLSL shaders which specify the
varyings using enhanced layouts. We were returning the info as if the
varyings could only be specified using the API.

  2. ARB_gl_spirv:

TRANSFORM_FEEDBACK_VARYING_MAX_LENGTH should return 1 if there is no
name reflection information available.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>