Finalize text of per-profile IME settings

This is a follow up CL to a recent CL [1], which updated text in the
Settings app as follows:
 * "Keyboard & inputs" to "Keyboards"
 * "Input assistance" to "Tools"

For consystency, this CL updates the header text for the work-profile
specific enties in Languages & input from
  Work profile input & assistance
to
  Work profile keyboards & tools.

Other than that, there is no user-visible behavior change.

 [1]: Idbf1e3a8b0c7116271e424548ef37340199eaea2
      5b27d18e

Bug: 124049901
Fix: 123314089
Test: Manually verified as follows.
  1. Build and flash an AOSP build
  2. Install Test DPC
  3. Open Settings -> System -> Languages & input
  4. Make sure that the new category header for work-profile specific
     entries is now shown as "Work profile keyboards & tools"
Change-Id: Ib6470debe9be29ec0985cf1e3eb31d232c6b3880