Refactor: WM: Suspend new jobs based on same job type, not callback

The callback-based identification was introduced before job types were added in
7b60529517. The job type should be a more predictable/sane way to identify jobs
that should be exclusive. Using anything else is confusing and non-obvious from
the API usage side. In fact it really confused me when working on #123027.

Checked all existing jobs to make sure behavior is unchanged. Found
two issues:
- `WM_JOB_TYPE_OBJECT_SIM_FLUID` is used for both
  `fluid_bake_startjob()` and `fluid_free_startjob()`. It makes sense to
  me that they would be exclusive though, so leaving it this way
  (meaning they are exclusive now).
- Alembic and USD job types were reused, split them up now to not change
  behavior.

Pull Request: https://projects.blender.org/blender/blender/pulls/123033

source/blender/io/alembic/exporter/abc_export_capi.cc

@@ -230,8 +230,12 @@ bool ABC_export(Scene *scene,
 
   bool export_ok = false;
   if (as_background_job) {
-    wmJob *wm_job = WM_jobs_get(
-        job->wm, CTX_wm_window(C), scene, "Alembic Export", WM_JOB_PROGRESS, WM_JOB_TYPE_ALEMBIC);
+    wmJob *wm_job = WM_jobs_get(job->wm,
+                                CTX_wm_window(C),
+                                scene,
+                                "Alembic Export",
+                                WM_JOB_PROGRESS,
+                                WM_JOB_TYPE_ALEMBIC_EXPORT);
 
     /* setup job */
     WM_jobs_customdata_set(wm_job, job, MEM_freeN);

source/blender/io/alembic/intern/alembic_capi.cc

@@ -746,7 +746,7 @@ bool ABC_import(bContext *C, const AlembicImportParams *params, bool as_backgrou
                                 job->scene,
                                 "Alembic Import",
                                 WM_JOB_PROGRESS,
-                                WM_JOB_TYPE_ALEMBIC);
+                                WM_JOB_TYPE_ALEMBIC_IMPORT);
 
     /* setup job */
     WM_jobs_customdata_set(wm_job, job, import_freejob);

source/blender/io/usd/intern/usd_capi_export.cc

@@ -641,7 +641,7 @@ bool USD_export(bContext *C,
   bool export_ok = false;
   if (as_background_job) {
     wmJob *wm_job = WM_jobs_get(
-        job->wm, CTX_wm_window(C), scene, "USD Export", WM_JOB_PROGRESS, WM_JOB_TYPE_ALEMBIC);
+        job->wm, CTX_wm_window(C), scene, "USD Export", WM_JOB_PROGRESS, WM_JOB_TYPE_USD_EXPORT);
 
     /* setup job */
     WM_jobs_customdata_set(wm_job, job, MEM_freeN);

source/blender/io/usd/intern/usd_capi_import.cc

@@ -521,7 +521,7 @@ bool USD_import(bContext *C,
                                 job->scene,
                                 "USD Import",
                                 WM_JOB_PROGRESS,
-                                WM_JOB_TYPE_ALEMBIC);
+                                WM_JOB_TYPE_USD_IMPORT);
 
     /* setup job */
     WM_jobs_customdata_set(wm_job, job, import_freejob);

source/blender/windowmanager/WM_api.hh

@@ -1589,7 +1589,10 @@ enum eWM_JobType {
   WM_JOB_TYPE_SEQ_BUILD_PREVIEW,
   WM_JOB_TYPE_POINTCACHE,
   WM_JOB_TYPE_DPAINT_BAKE,
-  WM_JOB_TYPE_ALEMBIC,
+  WM_JOB_TYPE_ALEMBIC_IMPORT,
+  WM_JOB_TYPE_ALEMBIC_EXPORT,
+  WM_JOB_TYPE_USD_IMPORT,
+  WM_JOB_TYPE_USD_EXPORT,
   WM_JOB_TYPE_SHADER_COMPILATION,
   WM_JOB_TYPE_STUDIOLIGHT,
   WM_JOB_TYPE_LIGHT_BAKE,
@@ -1609,8 +1612,8 @@ enum eWM_JobType {
 /**
  * \return current job or adds new job, but doesn't run it.
  *
- * \note every owner only gets a single job,
- * adding a new one will stop running job and when stopped it starts the new one.
+ * \note every owner only gets a single running job of the same \a job_type (or with the
+ * #WM_JOB_EXCL_RENDER flag). Adding a new one will wait for the running job to finish.
  */
 wmJob *WM_jobs_get(wmWindowManager *wm,
                    wmWindow *win,
@@ -1654,8 +1657,17 @@ void WM_jobs_callbacks_ex(wmJob *wm_job,
                           void (*canceled)(void *));
 
 /**
- * If job running, the same owner gave it a new job.
- * if different owner starts existing #wmJob::startjob, it suspends itself.
+ * Register the given \a wm_job and try to start it immediately.
+ *
+ * The new \a wm_job will not start immediately and wait for other blocking jobs
+ * to end in some way if:
+ * - the new job is flagged with #WM_JOB_EXCL_RENDER and another job with the same flag is already
+ *   running (blocks it), or...
+ * - the new job is __not__ flagged with #WM_JOB_EXCL_RENDER and a job of the same #eWM_JobType is
+ *   already running (blocks it).
+ *
+ * If the new \a wm_job is flagged with #WM_JOB_PRIORITY, it will request other blocking jobs to
+ * stop (using #WM_jobs_stop(), so this doesn't take immediate effect) rather than finish its work.
  */
 void WM_jobs_start(wmWindowManager *wm, wmJob *wm_job);
 /**

source/blender/windowmanager/intern/wm_jobs.cc

@@ -419,9 +419,9 @@ static void wm_jobs_test_suspend_stop(wmWindowManager *wm, wmJob *test)
         continue;
       }
 
-      /* If new job is not render, then check for same startjob. */
+      /* If new job is not render, then check for same job type. */
       if (0 == (test->flag & WM_JOB_EXCL_RENDER)) {
-        if (wm_job->startjob != test->startjob) {
+        if (wm_job->job_type != test->job_type) {
           continue;
         }
       }