Allow ITradeInMode to be used on ro.debuggable builds.

If persist.adb.test_tradeinmode is 1, then trade-in mode is allowed on
ro.debuggable=1 builds.

Bug: 379970773
Test: adb shell tradeinmode testing start
Flag: com.android.tradeinmode.flags.enable_trade_in_mode
Change-Id: Id6ae7d53aadd5e65d87d18cb86040a5b185f1b78