Summary
-------

Add `com.sun.management.ThreadMXBean::getCurrentThreadAllocatedBytes`.

Problem
-------

com.sun.management.ThreadMXBean includes getThreadAllocatedBytes in two versions, one which takes a thread_id and another which takes an array of thread_ids.
```
getThreadAllocatedBytes(long id);
getThreadAllocatedBytes(long[] ids);
```
It also includes versions of getThreadCpuTime and getThreadUserTime that take an array of thread_ids.
```
getThreadCpuTime(long[] ids);
getThreadUserTime(long[] ids);
```
java.lang.thread.ThreadMXBean defines single thread_id and current thread versions of these.
```
getThreadCpuTime(long id);
getThreadUserTime(long id);
getCurrentThreadCpuTime();
getCurrentThreadUserTime();
```
Three versions of Cpu and User time are thus available from com.sun.management.ThreadMXBean: current thread, single thread_id, and an array of thread_ids. Only two versions of AllocatedBytes are currently available: single thread_id and an array of thread_ids.

The current thread versions of Cpu and User time are optimized to by avoiding checks needed by the versions that take thread_id(s). getCurrentThreadAllocatedBytes can also be so optimized, is useful for applications that monitor themselves, and rounds out the set of AllocatedBytes methods. As with the other AllocatedBytes methods, getCurrentThreadAllocatedBytes is a method on com.sun.management.ThreadMXBean rather than java.lang.thread.ThreadMXBean in order to avoid requiring all implementations to support it.

Solution
--------

Add `com.sun.management.ThreadMXBean::getCurrentThreadAllocatedBytes`.

Specification
-------------
```
/**
 * Returns an approximation of the total amount of memory, in bytes,
 * allocated in heap memory for the current thread.
 * The returned value is an approximation because some Java virtual machine
 * implementations may use object allocation mechanisms that result in a
 * delay between the time an object is allocated and the time its size is
 * recorded.
 *
 * <p>
 * This is a convenience method for local management use and is
 * equivalent to calling:
 * <blockquote><pre>
 *   {@link #getThreadAllocatedBytes getThreadAllocatedBytes}(Thread.currentThread().getId());
 * </pre></blockquote>
 *
 * @return an approximation of the total memory allocated, in bytes, in
 * heap memory for the current thread
 * if thread memory allocation measurement is enabled;
 * {@code -1} otherwise.
 *
 * @throws java.lang.UnsupportedOperationException if the Java virtual
 *         machine implementation does not support thread memory allocation
 *         measurement.
 *
 * @see #isThreadAllocatedMemorySupported
 * @see #isThreadAllocatedMemoryEnabled
 * @see #setThreadAllocatedMemoryEnabled
 * @since 14
 */
public long getCurrentThreadAllocatedBytes();
```