[Full-stack Signals][DX] Add StringSignal type to store a shared text with collaborative capabilities

[taefi]

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Describe your motivation

We could have StringSignal that basically can store a collaborative text. This signal can have methods for text modifications, e.g. to insert at certain positions, to replace, or modify by regexp etc.

Describe the solution you'd like

No response

Describe alternatives you've considered

For starters, maybe, a more versatile ListSignal<Character> could support some of the needed API for a convenient support of such shared text data structure.

Additional context

No response