Touch up enableWriteAheadLogging javadoc

Lead with the benefits of WAL and best practices for apps.
Explain that WAL is beneficial even outside of concurrent access.
De-emphasize the added memory cost,
it's insignificant in today's devices vs the benefits of WAL.

Bug: 417797658
Flag: EXEMPT javadoc
Change-Id: I8472f0899cdc6bb37ba5e2a9df114373781da3a7