Autocomplete: Make string distance filters more lenient

[philipp-spiess]

We have gotten reports for cases where Cody didn't suggest a useful completion. One such case can be reproed with this example:

interface DoInteractionRequest {
    chatId: string
    prompt: string
    systemPrompt: string
}

interface Fuzz {
    string: () => string
}

const z: Fuzz = {} as any

const interactionRequest: DoInteractionRequest = {
    chatId█
    prompt: z.string(),
    systemPrompt: z.string(),
}

This was caused by the string distance between the inserted line chatId: z.string(), and the next line systemPrompt: z.string(), (or the one above, for that matter) to be too close. We use to guard heavily against it since our initial Claude Instant implementation could not do infilling well and was repeating the suffix in many cases.

Since we have infilling now, we can make this overlap much more lenient. This PR changes the threshold from 0.33% to 0.2%.

Test plan

Screen.Recording.2023-10-05.at.10.48.50.mov