Docs: show enum and bitflag values in comments only for special values

[kainino0x]

Generally users shouldn't be particularly interested in the numeric values of enums and bitflags except for special cases. It makes more sense to highlight those so they stick out, rather than blending into the noise.

• Undefined=0 / BindingNotUsed=0, because it's what you get from zero-init
• Undefined=1, because it's an exception to the usual
• Bitflags that are 0 or combinations (All=Red|Green|Blue|Alpha)