9.6.4.5: Clarify that @SuppressWarnings requires unknown strings to be ignored

The API specification for java.lang.SuppressWarnings states:

"The presence of unrecognized warning names is not an error: Compilers must ignore any warning names they do not recognize. They are, however, free to emit a warning if an annotation contains an unrecognized warning name."
https://docs.oracle.com/en/java/javase/13/docs/api/java.base/java/lang/SuppressWarnings.html#value()

This requirement to ignore unknown strings is not included in JLS 9.6.4.5. @SuppressWarnings. The JLS and API spec should be consistent in the requirements on compilers in handling the annotation.