Invalidate dependency targets for jvmdoc if --combined. (#7455)

### Problem

The doc.scaladoc task (and likely also the doc.javadoc task), when used with --combined is skipping dependencies in the graph during the 'invalidation' stage, because it is not passing invalidate_dependents in the docable predicate that is part of the base class JvmDocGen.

See issue: #7434

### Solution

In the relevant spot in `JvmDocGen` class, this change passes the `invalidate_dependents` parameter to `self.invalidate()` with attribute `self.combined` for the value which is `True` for combined doc builds and `False` otherwise. 

### Result

This causes the invalidation logic to behave as expected, specifically, invalidating the dependencies within the entire graph for a combined doc build. I tested this locally to ensure the correct behavior, and ran all relevant unit tests.

src/python/pants/backend/jvm/tasks/jvmdoc_gen.py

@@ -111,18 +111,25 @@ def docable(target):
     if not targets:
       return
 
-    with self.invalidated(targets) as invalidation_check:
-      def find_jvmdoc_targets():
+    with self.invalidated(targets, invalidate_dependents=self.combined) as invalidation_check:
+      def find_invalid_targets():
         invalid_targets = set()
         for vt in invalidation_check.invalid_vts:
           invalid_targets.update(vt.targets)
         return invalid_targets
 
-      jvmdoc_targets = list(find_jvmdoc_targets())
-      if self.combined:
-        self._generate_combined(jvmdoc_targets, create_jvmdoc_command)
-      else:
-        self._generate_individual(jvmdoc_targets, create_jvmdoc_command)
+      invalid_targets = list(find_invalid_targets())
+      if invalid_targets:
+        if self.combined:
+          self._generate_combined(targets, create_jvmdoc_command)
+        else:
+          self._generate_individual(invalid_targets, create_jvmdoc_command)
+
+    if self.open and self.combined:
+      try:
+        desktop.ui_open(os.path.join(self.workdir, 'combined', 'index.html'))
+      except desktop.OpenError as e:
+        raise TaskError(e)
 
     if catalog:
       for target in targets:
@@ -142,11 +149,6 @@ def _generate_combined(self, targets, create_jvmdoc_command):
         self.context.log.debug("Running create_jvmdoc in {} with {}".format(gendir, " ".join(command)))
         result, gendir = create_jvmdoc(command, gendir)
         self._handle_create_jvmdoc_result(targets, result, command)
-    if self.open:
-      try:
-        desktop.ui_open(os.path.join(gendir, 'index.html'))
-      except desktop.OpenError as e:
-        raise TaskError(e)
 
   def _generate_individual(self, targets, create_jvmdoc_command):
     jobs = {}