assistant2: Allow profiles to enable all context servers (#27847)

This PR adds a new `enable_all_context_servers` field to agent profiles
to allow them to enable all context servers without having to opt into
them individually.

The "Write" profile will now have all context servers enabled out of the
box.

Release Notes:

- N/A

crates/assistant_tool/src/tool_working_set.rs

@@ -19,6 +19,7 @@ pub struct ToolWorkingSet {
 struct WorkingSetState {
     context_server_tools_by_id: HashMap<ToolId, Arc<dyn Tool>>,
     context_server_tools_by_name: HashMap<String, Arc<dyn Tool>>,
+    enabled_sources: HashSet<ToolSource>,
     enabled_tools_by_source: HashMap<ToolSource, HashSet<Arc<str>>>,
     next_tool_id: ToolId,
 }
@@ -168,21 +169,22 @@ impl WorkingSetState {
     }
 
     fn enable_source(&mut self, source: ToolSource, cx: &App) {
-        let tools_by_source = self.tools_by_source(cx);
-        let Some(tools) = tools_by_source.get(&source) else {
-            return;
-        };
+        self.enabled_sources.insert(source.clone());
 
-        self.enabled_tools_by_source.insert(
-            source,
-            tools
-                .into_iter()
-                .map(|tool| tool.name().into())
-                .collect::<HashSet<_>>(),
-        );
+        let tools_by_source = self.tools_by_source(cx);
+        if let Some(tools) = tools_by_source.get(&source) {
+            self.enabled_tools_by_source.insert(
+                source,
+                tools
+                    .into_iter()
+                    .map(|tool| tool.name().into())
+                    .collect::<HashSet<_>>(),
+            );
+        }
     }
 
     fn disable_source(&mut self, source: &ToolSource) {
+        self.enabled_sources.remove(source);
         self.enabled_tools_by_source.remove(source);
     }