Remove a dependency on IMM#isActive() from Editor.java

Despite its name, InputMethodManager#isActive(View) internally aquires
IMM lock three times and may even trigger IME focus switching.

To make things simpler and more predictable,

  InputMethodManager#hasActiveInputConnectionInternal()

should be used instead.

Bug: 291826769
Bug: 287109569
Test: presubmit
Change-Id: Iad75edd76de5957819f0dca14bdb4068c14a09a1