Make SelectionActionModeHelper hardcoded constants configurable.

Read the selection timeout value from ViewConfiguration,
ViewConfiguration is statically configurable by the OEM. OEMs can
set the value which works on their device before shipping it.

After privacy sync, we can make the selection context size
configurable by DeviceConfig but we need to provide a
reasonable upper bound. The value is 240 after experiment.

Bug: 169042855
Test: atest CtsTextClassifierTestCases
Test: atest CtsWidgetTestCases:TextViewTest
Test: atest android.widget.TextViewActivityTest
Test: manual. Changes values by command and checks the values.

Change-Id: I59346fdc3b482bca586c13ba6c653d1e9b593922