After `Settings > System > Languages & input` was separated into
`Settings > System > Languages` and `Settings > System > Keyboard`,
`On-device speech recognition` was lost. This CL adds it in the same
`Speech` preference category where it was before
and moves the category to `Settings > System > Languages`.
Bug: 278279110
Test: Manual, already existing robotests
Change-Id: I040c284dd3596f35ceacb6980ff89e611e29971c
1. Separate "Keyboard" from "Language & input".
2. Use FeatureFlagUtils.SETTINGS_NEW_KEYBOARD_UI to control the
different UI until Settings launches the new UI design.
Bug: 242680328
Test: local test
Change-Id: Id1ea6d3e3c2e6b83bc4b4d835c6b27e31311c530
