TextUnmarshaler support for binding

[ssoroka]

• Adds encoding.TextUnmarshaler checking to support unmarshaling custom non-struct types.
• Adds binding.BindUnmarshaler to support unmarshaling custom structs (from the suggestion in #2673)

As of this PR you can support any kind of custom type without breaking support for time.Time and other structs that might implement TextUnmarshaler

Closes #2673 Closes #2631

[ssoroka]

@kszafran I think I've addressed all your feedback. Mind taking another look?

[ssoroka]

@thinkerou when you have a chance, could you review/merge/tag another maintainer?

[amahiwa-jp]

Looks like an essential feature to have. @ssoroka Could you squash your commits as requested per CONTRIBUTING.md? @thinkerou @appleboy Could you check out this when you have time?

[ssoroka]

@amahiwa-jp I've squashed the commits into a single commit

[dcrystalj]

ETA for this?

[duaneking]

Updates?

[brokeyourbike]

Any update on when it can be merged?

[steveadams]

Is there anything I can contribute to help get this merged?

[AnatolyUA]

To make it work with arrays []uuid.UUID we might add to func setWithProperType:

	case reflect.Array:
		if a, e := trySetCustom(val, value); a || e != nil {
			return e
		}
		return errUnknownType

[eloyekunle]

Any update on this?

[minghan9456]

Any update?

[duaneking]

What are the perf changes for this update?

How much does it slow down binding for other things?

[phenixrizen]

@appleboy @thinkerou @javierprovecho Any update on this?

[duaneking]

Again, What is the perf change of this?

Have you done the work to assure it does not slow other things down?

[ssoroka]

I don't see any performance impact to this. I've been using this in production for a year and a half at this point. Maybe someone could pick it up, update it, and merge it?

[appleboy]

@ssoroka I don't know why I can't review the PR? Can you create a new PR?