Truncate(*1) it if WAL file is too big when opening DB

*1 -- not truncate(2) but "PRAGMA wal_checkpoint(TRUNCATE)"

Otherwise, depending on how an app operate on a DB, SQLite may not
have a chance to "shrink" the WAL file.

Fixes: 112777941
Bug: 111939259
Test: atest /android/master/frameworks/base/core/tests/coretests/src/android/database/sqlite/SQLiteCompatibilityWalFlagsTest.java
Test: Manual test with google dailer:
1. With normalized_spam.db-wal > 100MB and receive a phone call
-> WAL file gets truncated to 0 bytes.

2. Restart the dialer process and receive a phone call again
-> WAL file is already 0 bytes; won't be truncated.

3. Restart with the WAL file deleted
Same as #2. WAL file will be created before the added logic, but is 0 bytes,
so it won't be truncated.

4. Test with settings put global sqlite_compatibility_wal_flags truncate_size=1024
-> make sure the threshold is overridden

Change-Id: I2b193603e5dfa493ccccb8123db592f0e9c0e7ae