Disallow scrolling tan entry text view (closes #546) (#588)

* Implemented a UnscrollableEditText which resets selection to text end on change

Signed-off-by: Kolya Opahle <k.opahle@sap.com>

* Added import for AppCompatEditText

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/ui/view/UnscrollableEditText.kt

+package de.rki.coronawarnapp.ui.view
+
+import android.content.Context
+import android.util.AttributeSet
+import androidx.appcompat.widget.AppCompatEditText
+
+class UnscrollableEditText(context: Context, attributeSet: AttributeSet) :
+    AppCompatEditText(context, attributeSet) {
+    override fun onSelectionChanged(selStart: Int, selEnd: Int) {
+        super.onSelectionChanged(selStart, selEnd)
+        text?.length?.let { setSelection(it) }
+    }
+}

Corona-Warn-App/src/main/res/layout/view_tan_input_edittext.xml

 <?xml version="1.0" encoding="utf-8"?>
 <layout xmlns:android="http://schemas.android.com/apk/res/android">
 
-    <EditText
+    <de.rki.coronawarnapp.ui.view.UnscrollableEditText
         android:id="@+id/tan_input_edittext"
         style="@style/tanInputEdittext" />