Add completion possibilities that split the current token

Consider the following (where the vertical line represents the cursor position):

program = dr|codeWorldLogo

Triggering autocomplete will now try to match the entire token, `drcodeWorldLogo`. Autocomplete will decide that `drawingOf` is the best suggestion by far, and turn the whole thing into `drawingOf`. The `codeWorldLogo` is lost.

Instead, auto-complete should be willing to also consider splitting the token into `dr` (before the cursor) and `codeWorldLogo` at the end. If they are BOTH close to existing tokens, then autocomplete should potentially replace the `dr` with `drawingOf`, and leave `codeWorldLogo` alone. The decision about whether to split the current token or not should be made based on the edit distance to turn the portion after the cursor into a known token, as compared to the edit cost of deleting it after this completion, possibly with some weighting in favor of one or the other choice.

Nell’issue non sono indicati file di implementazione né test. Inizia individuando il codice di autocomplete che corrisponde al token corrente e alla relativa logica della distanza di edit, quindi segui il modo in cui il cursore divide il token. Il lavoro è completato quando autocomplete può confrontare la sostituzione dell’intero token con la divisione prima del cursore, preservare un suffisso valido e scegliere in modo coerente tra le alternative.

Scritto dal modello di indicizzazione a partire dal testo della issue.