mesa: Add function to calculate an orthographic projection

mesa: Add function to calculate an orthographic projection

Unlike the existing _math_matrix_ortho, the new _math_float_ortho
function just stores the calculated matrix in an array of floats.  It
does not multiply the new matrix with data already stored.

   text     data     bss      dec    hex  filename
12243486 1344936 1290748 14879170 e309c2  before/lib64/dri/i965_dri.so
12243510 1344936 1290748 14879194 e309da  after/lib64/dri/i965_dri.so

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/856>