Use separate receivers for managing the intent registerations

- Added the utility `TestUtil` class for managing common functions among the pairing tests, such as getProfileProxy(), removeBond(), etc.
- Updated `EncryptionChangeTest` class with `IntentReceiver` utility usage.
- Updated `PairingTest` with common functions moved to `TestUtil`.

Change-Id: I2e7a2a8a7c8027563cf98c890fa05d4918a43f90
Test: atest PairingTest, EncryptionChangeTest
Flag: TEST_ONLY
Bug: 388810455