[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, 11 insertions, 4 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/lldbtest.py b/lldb/packages/Python/lldbsuite/test/lldbtest.py
index a4ff96e..63fadb5 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbtest.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbtest.py
@@ -2268,7 +2268,7 @@ class TestBase(Base, metaclass=LLDBTestCaseFactory):
             completions, list(match_strings)[1:], "List of returned completion is wrong"
         )
 
-    def completions_contain(self, command, completions):
+    def completions_contain(self, command, completions, match=True):
         """Checks that the completions for the given command contain the given
         list of completions."""
         interp = self.dbg.GetCommandInterpreter()
@@ -2276,9 +2276,16 @@ class TestBase(Base, metaclass=LLDBTestCaseFactory):
         interp.HandleCompletion(command, len(command), 0, -1, match_strings)
         for completion in completions:
             # match_strings is a 1-indexed list, so we have to slice...
-            self.assertIn(
-                completion, list(match_strings)[1:], "Couldn't find expected completion"
-            )
+            if match:
+                self.assertIn(
+                    completion,
+                    list(match_strings)[1:],
+                    "Couldn't find expected completion",
+                )
+            else:
+                self.assertNotIn(
+                    completion, list(match_strings)[1:], "Found unexpected completion"
+                )
 
     def filecheck(
         self, command, check_file, filecheck_options="", expect_cmd_failure=False