Add InputConnection debug information

Add InputConnection information to IME tracing. This change adds
only information about the text associated with an
EditableInputConnection instance: editable text, selected text, text
before and after the cursor (for a preset length) and cursor caps mode.

Test: flash a device
      start IME tracing with `adb shell ime tracing start`
      stop IME tracing with `adb shell ime tracing stop`
      visualise the traces in Winscope and see the inputConnection information
Change-Id: I4dc6147fb7baa2cea413d2c44226e8c84c056c37