Implement readahead cache for Workspace API calls (#1582)

## Changes

The reason this readahead cache exists is that we frequently need to
recursively find all files in the bundle root directory, especially for
sync include and exclude processing. By caching the response for every
file/directory and frontloading the latency cost of these calls, we
significantly improve performance and eliminate redundant operations.

## Tests

* [ ] Working on unit tests

Author: pietern