mesa/main: fix validation of transform-feedback queries

mesa/main: fix validation of transform-feedback queries

ctx->Extensions.EXT_transform_feedback is set based on the driver-
capabilities, not based on the context type. We need to check against
_mesa_has_EXT_transform_feedback(ctx) instead to figure out if the
extension is really supported. We also need to check for
OES_geometry_shader.

This turns usage of GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN into an
error on ES 2, as well as usage of GL_PRIMITIVES_GENERATED on ES 3, both
as required by the spec.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>