mesa,glsl: rename `interface` to `programInterface`.

mesa,glsl: rename `interface` to `programInterface`.

`interface` is a define on Windows -- an alias for `struct` keyword,
used when declaring COM interfaces in C or C++.

So use instead `programInterface`, therefore matching the name used
in GL_ARB_program_interface_query spec/headers, which was renamed exactly
for the same reason:

  "Revision 10, May 10, 2012 (pbrown)
     - Rename the formal parameter <interface> used by the functions in this
       extension to <programInterface>.  Certain versions of the Microsoft
       C/C++ compiler and/or its headers cause "interface" to be treated as a
       reserved keyword."

Trivial.