Add support for concatenating values by keys

[Kortvk]

Introduce the ability to construct strings using existing keys. Example:

[key_1]
  en = value 1
[key_2]
  en = value 2
[key_3]
  en = %ref(key_1) some text %ref(key_2)

Further consideration is needed on how to handle situations where key_1 and key_2 have formatting. In such cases, it can be resolved as follows:

[key_1]
  en = text 1.1 %2$s text 1.2 %1$s
[key_2]
  en = text 2.1 %2$s text 2.2 %1$s
[key_3]
  en = %ref(key_1, 1, 2) some text %ref(key_2, 3, 4)

Where the values after the key name indicate the order of the passed values to ensure consistency regardless of the formatting used within the keys.

[dimsuz]

I'm not sure if there is a good reason to add this feature.

This can easily be done:

[key_1]
  en = value 1
[key_2]
  en = value 2
[key_3]
  en = %s some text %s

and then user can substitute in code (for example in Android):

getString(R.key_3, getString(R.string.key_1), getString(R.strings.key_2)

User is also free to write their own utility functions such as:

getCompositeString(R.string.key_3, R.string.key_1, R.string.key_2)

etc.

Adding refs as a feature in utas would introduce unnecessarily complications, we would have to also think about how to resolve these refs recursively: what if key_1 and key_2 are also using refs? What if there are cycles?

I'd vote to follow platforms (ios/android) more closely here: they do not allow refs like these.

[TrueWarg]

@Kortvk, you really can achieve first case using kotlin side code as @dimsuz mentioned.
But I haven't catched idea of the second. Could you please write some example, maybe it's can be made on kotlin side too?