Pass `-XDaddTypeAnnotationsToSymbol=true` as a javac argument?

[msridhar]

See uber/NullAway#1245. This javac argument improves NullAway's ability to read type use annotations from bytecodes on JDK 21.0.8 (or later, presumably), which is particularly helpful in JSpecify mode. It may be useful for other built-in Error Prone checks to also be able to see these annotations, though I'm not sure; possibly @cpovirk or @cushon could comment? This flag may also be ported back to JDK 17 in the future.

The downside is that in some (rare?) cases this flag can cause build issues; see https://bugs.openjdk.org/browse/JDK-8359336. Given that, I'm not sure whether enabling this flag by default with the Error Prone plugin is the right approach. But it would be nice if it were at least exposed as an opt-in option of the Error Prone plugin, to give it more visibility.

Also, FWIW, I saw no negative consequences to passing this flag to javac versions other than 21.0.8; it seems to just be ignored.