Allow apps to write to the clipboard without input focus

Blocking writes breaks common share UI flow in apps. Since common
write abuse cases rely on modifying the contents (e.g. injecting spam
links) only blocking reads still gives the intended privacy properties.

Test: atest tests/tests/content/src/android/content/cts/ClipboardManagerTest.java
Fixes: 112844309

Change-Id: I18fdba192fcf9c8d3fb4cbaeaea1468657e5131e