Support incremental parsing for autocomplete

Right now, the autocomplete channel accepts the entire file every time without providing the runner plugin any hint to the actual ranges of changes made. This causes the entire file to be reparsed every keypress

The frontend should be able to send the ranges of changes made between requests.
An example is
```
a = 1
```
to 
```
a = 100
```
Would return `[{fromA: 4, toA: 5, fromB: 4, toB: 7}]`