perf: API docs: do not rerender entire page when searching

Created by: slimsag

React.FunctionComponent always rerenders the component, even if props have not changed. This is an issue with a LOT of components in Sourcegraph, and in the case of API docs surfaces as "typing in the search bar makes the entire page stall/stutter/lag"

This fixes it by using React.memo, see #21200 (closed) for details.

Helps #21200 (closed)

Signed-off-by: Stephen Gutekanst [email protected]