Native bindings to the OES_texture_half_float extension.

These extensions add texture formats with 16- (aka half float) and 32-bit floating-point components. The 32-bit floating-point components are in the standard IEEE float format. The 16-bit floating-point components have 1 sign bit, 5 exponent bits, and 10 mantissa bits. Floating-point components are clamped to the limits of the range representable by their format.

The OES_texture_half_float extension string indicates that the implementation supports 16-bit floating pt texture formats.

Both these extensions only require NEAREST magnification filter and NEAREST, and NEAREST_MIPMAP_NEAREST minification filters to be supported.