Use LocaleUtils#filterByLanguage for non-keyboard subtypes.

With this CL, we expand the target of Bug 27129703 and Bug 27348943 to
non-keyboard subtypes.

Suppose there is a handwriting IME (mode == "handwriting") that supports
the following 5 subtypes.
  - en-US
  - en-GB
  - fr
  - sr-Cyrl
  - sr-Latn

Also suppose the system languages are configured as follows.
  1. sr-Latn-RS
  2. ja-JP
  3. fr-FR
  4. en-GB
  5. en-US

In this case we want to enable [sr-Latn, fr, en-GB] by default when
"use system language" is checked in the subtype enabler.

See previous commits [1][2] about how we addressed those issues for
keyboard subtypes.

  [1]: Iaf179d60c12b9a98b4f097e2449471c4184e049b
       e985c240
  [2]: I8fc774154f5175abff2f16e8f12a4847bf5f5b7c
       072a95a3

Bug: 27560993
Change-Id: I416b5671602c550805ed6267dd210968aa1de83c