Rename IME_SHOWN states to IME_VISIBLE

This renames the SysUI states related to the IME and IME Switcher button
visibility from "shown" to "visible", to maintain consistency.

Flag: EXEMPT refactor
Bug: 366129400
Test: n/a
Change-Id: I45219e62b633ca984de98df43f5c238604b38109
5 files changed