Broken links in java.util.concurrent.atomic

A link checker has found these broken links:

api/java.base/java/util/concurrent/atomic/AtomicIntegerFieldUpdater.html:487: id not found: api/java.base/java/util/concurrent/atomic/package-summary.html#weakCompareAndSet
api/java.base/java/util/concurrent/atomic/AtomicLongFieldUpdater.html:487: id not found: api/java.base/java/util/concurrent/atomic/package-summary.html#weakCompareAndSet
api/java.base/java/util/concurrent/atomic/AtomicMarkableReference.html:375: id not found: api/java.base/java/util/concurrent/atomic/package-summary.html#weakCompareAndSet
api/java.base/java/util/concurrent/atomic/AtomicReferenceFieldUpdater.html:453: id not found: api/java.base/java/util/concurrent/atomic/package-summary.html#weakCompareAndSet
api/java.base/java/util/concurrent/atomic/AtomicStampedReference.html:375: id not found: api/java.base/java/util/concurrent/atomic/package-summary.html#weakCompareAndSet

Although not P3 in themselves, they are part of the noise preventing us achieving a goal of no broken links.

Also, these references are causing broken links.

open/src/java.base/share/classes/java/util/concurrent/atomic/LongAccumulator.java: * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.LongAccumulator.SerializationProxy">
open/src/java.base/share/classes/java/util/concurrent/atomic/DoubleAccumulator.java: * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.DoubleAccumulator.SerializationProxy">
open/src/java.base/share/classes/java/util/concurrent/atomic/LongAdder.java: * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.LongAdder.SerializationProxy">
open/src/java.base/share/classes/java/util/concurrent/atomic/DoubleAdder.java: * <a href="../../../../serialized-form.html#java.util.concurrent.atomic.DoubleAdder.SerializationProxy">

There's a missing "../" at the beginning of the relative URL, but a better solution is to replace all the ../ with just `{@docRoot}`