[lldb] Add completions for plugin list/enable/disable (#147775)

This commit adds completion support for the plugin commands. It will try
to complete partial namespaces to the full namespace string. If the
completion input is already a full namespace string then it will add all
the matching plugins in that namespace as completions.

This lets the user complete to the namespace first and then tab-complete
to the next level if desired.

```
(lldb) plugin list a<tab>
Available completions:
        abi
        architecture
(lldb) plugin list ab<tab>
(lldb) plugin list abi<tab>
(lldb) plugin list abi.<tab>
Available completions:
        abi.SysV-arm64
        abi.ABIMacOSX_arm64
        abi.SysV-arm
        ...
```

1 files changed, 8 insertions, 0 deletions

diff --git a/lldb/source/Commands/CommandCompletions.cpp b/lldb/source/Commands/CommandCompletions.cpp
index 38231a8..3e22309 100644
--- a/lldb/source/Commands/CommandCompletions.cpp
+++ b/lldb/source/Commands/CommandCompletions.cpp
@@ -87,6 +87,7 @@ bool CommandCompletions::InvokeCommonCompletionCallbacks(
       {lldb::eTypeCategoryNameCompletion,
        CommandCompletions::TypeCategoryNames},
       {lldb::eThreadIDCompletion, CommandCompletions::ThreadIDs},
+      {lldb::eManagedPluginCompletion, CommandCompletions::ManagedPlugins},
       {lldb::eTerminatorCompletion,
        nullptr} // This one has to be last in the list.
   };
@@ -850,6 +851,13 @@ void CommandCompletions::ThreadIDs(CommandInterpreter &interpreter,
   }
 }
 
+void CommandCompletions::ManagedPlugins(CommandInterpreter &interpreter,
+                                        CompletionRequest &request,
+                                        SearchFilter *searcher) {
+  PluginManager::AutoCompletePluginName(request.GetCursorArgumentPrefix(),
+                                        request);
+}
+
 void CommandCompletions::CompleteModifiableCmdPathArgs(
     CommandInterpreter &interpreter, CompletionRequest &request,
     OptionElementVector &opt_element_vector) {