Fallback for empty local name

Since 2020 (https://r.android.com/1400927) native errors are no longer
reported, and notably, if the name is an empty value, the error is
silently discarded in the stack.

When setting a name that only contains spaces, this will work
temporarily until the stack restarts, read the config and trim the
output — since at least 2020 (https://r.android.com/1324998)

This CL does a couple things to address the issue.
* Warn the user at API level when the name result is an empty name
* Fallback to "Android" as local name if no property exist (unlikely)
* Use local name if config stored return in an empty string

This way we are preventing new wrong usage while also fixing existing
wrong config

also, nit cleanup on some native struct initialization

Bug: 393733290
Bug: 395178934
Test: atest CtsBluetoothTestCases
Test: manual set the name to null and check no crash
Flag: com.android.bluetooth.flags.empty_name_are_invalid
Change-Id: I0cb23cd26ca2273dcccda47e147183117777d920