Consistently use `TimeToLive` instead of TTL in public APIs

[PranavSenthilnathan]

I'm tempted to recommend the spelled-out DefaultTimeToLiveMs because DefaultTtlMs is tough to read, but I don't think my signal is strong enough to actually recommend it. Just a "worth considering for readability" suggestion instead.

Originally posted by @jeffhandley in #1579 (comment)