Editorial: add <dfn>s for "Job" and "Job Queue"

This will work a bit more cleanly once
tc39/ecmarkup#157 lands, and "Job Queues"
is picked up by ecmarkup.

spec.html

@@ -7493,7 +7493,7 @@ <h1>GetGlobalObject ( )</h1>
 
   <emu-clause id="sec-jobs-and-job-queues">
     <h1>Jobs and Job Queues</h1>
-    <p>A Job is an abstract operation that initiates an ECMAScript computation when no other ECMAScript computation is currently in progress. A Job abstract operation may be defined to accept an arbitrary set of job parameters.</p>
+    <p>A <dfn id="job">Job</dfn> is an abstract operation that initiates an ECMAScript computation when no other ECMAScript computation is currently in progress. A Job abstract operation may be defined to accept an arbitrary set of job parameters.</p>
     <p>Execution of a Job can be initiated only when there is no running execution context and the execution context stack is empty. A PendingJob is a request for the future execution of a Job. A PendingJob is an internal Record whose fields are specified in <emu-xref href="#table-25"></emu-xref>. Once execution of a Job is initiated, the Job always executes to completion. No other Job may be initiated until the currently running Job completes. However, the currently running Job or external events may cause the enqueuing of additional PendingJobs that may be initiated sometime after completion of the currently running Job.</p>
     <emu-table id="table-25" caption="PendingJob Record Fields">
       <table>
@@ -7567,7 +7567,7 @@ <h1>Jobs and Job Queues</h1>
         </tbody>
       </table>
     </emu-table>
-    <p>A Job Queue is a FIFO queue of PendingJob records. Each Job Queue has a name and the full set of available Job Queues are defined by an ECMAScript implementation. Every ECMAScript implementation has at least the Job Queues defined in <emu-xref href="#table-26"></emu-xref>.</p>
+    <p>A <dfn id="job-queue">Job Queue</dfn> is a FIFO queue of PendingJob records. Each Job Queue has a name and the full set of available Job Queues are defined by an ECMAScript implementation. Every ECMAScript implementation has at least the Job Queues defined in <emu-xref href="#table-26"></emu-xref>.</p>
     <p>Each agent has its own set of named Job Queues.  All references to a named job queue in this specification denote the named job queue of the surrounding agent.</p>
     <emu-table id="table-26" caption="Required Job Queues">
       <table>