This turns two methods with side-effects into more pure functions
with more obvious input and output. buildSearchIndex rebuilds the
internal search index from the internalList. buildSearchResults
filters and creates the result widgets the user will see.
This patch really only moves existing code around but doesn't change
anything. Except that this.built is set before onQueryChange is
called, not after. This avoids potential endless loops in case
onQueryChange happens to trigger buildIndex again.
Bug: T356871
Change-Id: Ib80a2dcb85779d64bec53caf90c49879d0ea2258