Add UNKNOWN_TO_SDK value to enums

[jderusse]

This PR asserts that enums returned by the API are wellknown values. Otherwise it fallback to the UNKNOWN_TO_SDK generic value.

In that way, we respect the contract when saying methods returns a FooEnum::*.

Side note: We still have to keep the psalm exceptions, because psalm can not infer the type of Enum::exists($value) ? $value : Enum:FALLBACK to Enum::*.

see https://psalm.dev/r/518a0924fe

We would need an equivalent of typescript's is keyword https://www.typescriptlang.org/docs/handbook/2/narrowing.html#using-type-predicates

fix #1921

[stof]

The static analysis can actually be fixed by using @psalm-assert-if-true: https://psalm.dev/r/b90672fbda

[jderusse]

Diff is huge.. Here is a summary:

1. added public const UNKNOWN_TO_SDK = 'UNKNOWN_TO_SDK'; in all Enums
2. added @psalm-assert-if-true self::* $value on all Enum's static function exists methods
3. in resutls: replaced $value by !TheEnum::exists($value) ? TheEnum::UNKNOWN_TO_SDK : $value.
4. in input: added /** @psalm-suppress NoValue */ after if (!TheEnum::exists($v)) { throw ... } because I want to keep the check even if the docbloc says $v is a TheEnum::* and I'm not sure we should relax the docblock to TheEnum::*|string