Prevent data races in reachability handlers registration when using
`-H:-RunReachabilityHandlersConcurrently`.

Closes oracle#5868

(cherry picked from commit 777cb82)

Don't allow null values to be passed to the `register` method of
`RuntimeJNIAccess` and `RuntimeReflection`. Since these are public APIs
GraalVM should either handle null values (by ignoring them in this case)
or throw a `NullPointerException` before creating an asynchronous task
to perform the registration in the analysis, which then results in
`NullPointerException`s being thrown later when it's no longer possible
to understand where the null value originate from.

(cherry picked from commit e6c12dd)

(cherry picked from commit d621dbd)

Not before the register methods, which can miss cases, nor later on in a runnable.

(cherry picked from commit f94551a)

(cherry picked from commit d996f32)

(cherry picked from commit 0ba6cc2)