Refactors`ui_text_remove_secondary_carets` from https://github.com/godotengine/godot/pull/68089 as `ui_text_clear_carets_and_selection`, with extra behaviour:
- If there's only one active caret active with a selection, clears the selection.
- In case there's more than one caret active, removes the secondary carets and clears selections.
With this change, `TextEdit` then imitates the behaviour of VSCode for clearing carets and selections.
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