compute: add regexp in-place replacement
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/26538.
Hooks up the replace behavior to the endpoint so that something like this works:
repo:sourcegraph/sourcegraph$ file:parser.go content:replace(Parse->derp)
.
Need some follow up changes to make things easier to use /test.