[core] Fix overspecialization of PaintPropertyBinder template

PaintPropertyBinder and subclass templates were being instantiated for every unique attribute type (e.g. a_color, a_fill_color, a_halo_color) even though they behave identically for a given property value type (e.g. Color). To fix this, a unique type such as a_color no longer derives from gl::Attribute<...> -- instead it has an inner Type typedef, which should be used wherever neither a unique type nor attribute name is required. This reduces binary size substantially:

     VM SIZE                               FILE SIZE
 ++++++++++++++ GROWING                 ++++++++++++++

 -------------- SHRINKING               --------------
  -2.0% -49.3Ki __TEXT,__text           -49.3Ki  -2.0%
  -3.1% -5.21Ki [None]                  -2.79Ki  -1.6%
  -2.1% -4.12Ki __TEXT,__const          -4.12Ki  -2.1%
  -1.4% -4.04Ki __TEXT,__gcc_except_tab -4.04Ki  -1.4%
 -19.3% -3.62Ki __DATA,__data           -3.62Ki -19.3%
  -2.5% -1.65Ki __TEXT,__unwind_info    -1.65Ki  -2.5%
  -4.2%      -8 __DATA,__mod_init_func        0  [ = ]

  -1.9% -68.0Ki TOTAL                   -65.6Ki  -1.9%

0 files changed, 0 insertions, 0 deletions