Use TestIme also in CtsTextTestCases

This commit aims to apply what we did [1][2][3] for CtsWidgetTestCases
in Bug 186526091 to CtsTextTestCases as well, instead of relying on
CtsKeyEventUtil [4].

TestIme gives a strong guarantee that 1) it will never be shown and 2)
it will never intercept hardware key events, which is in general a
better solution than relying on CtsKeyEventUtil, which only gives a
weak guarantee on hardware keyboard event dispatching.

Let's use TestIme also in CtsTextTestCases.

 [1]: I20ca55f1f7cde5451ce2a49926d019cced39b6a4
      1d0026ff911338557bc8c6292fa2eacb21121bd8
 [2]: I213cbc533df05eddd03f8a01c5577f24bc221095
      69e34bcc1fe5fe992b028996983cea513e77bfdf
 [3]: Ic7f494a0438d10ea5b015d379165df6622cae16b
      ab156450ad2491944fc7c98e159fd2520828f821
 [4]: Icbe68c965fb4869c39dd13f2afdcb2d4de872d22
      5bd6955fa69a7f5e07d669ea677840099c4e1dbc

Fix: 299176376
Test: atest CtsTextTestCases
Change-Id: I787c98e9f28bef723dac0d2d4099375a6258bc59