Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/5a5c3a5ac284
Author: Rudy Lu <me@rudy.lu>
Desc: Merge pull request #19619 from RudyLu/keyboard/Bug1010025-IME_switching_test

Bug 1010025 - Add integration test to cover 3rd-party IME Switching.
r=evanxd.

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https://hg.mozilla.org/integration/gaia-central/rev/dfdff974ce38
Author: Rudy Lu <me@rudy.lu>
Desc: Bug 1010025 - Add integration test to cover 3rd-party IME Switching.
 - Separate system app related part to lib/system.js

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https://hg.mozilla.org/integration/gaia-central/rev/64a5cef65ecc
Author: Min-Zhong "John" Lu <mnjul@users.noreply.github.com>
Desc: Merge pull request #20137 from mnjul/bug_1020115_lockscreen_vis_refresh_followup

Bug 1020115 - Lockscreen Visual Refresh follow-up [r=gweng]

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https://hg.mozilla.org/integration/gaia-central/rev/b3352f8d0de8
Author: John Lu [:mnjul] <jlu@mozilla.com>
Desc: Bug 1020115 - Lockscreen Visual Refresh follow-up
Bumping manifests a=b2g-bump