debugger: Add debug task picker to new session modal (#29702)

## Preview 

![image](https://github.com/user-attachments/assets/203a577f-3b38-4017-9571-de1234415162)


### TODO
- [x] Add scenario picker to new session modal
- [x] Make debugger start action open new session modal instead of task
modal
- [x] Fix `esc` not clearing the cancelling the new session modal while
it's in scenario or attach mode
- [x] Resolve debug scenario's correctly

Release Notes:

- N/A

crates/task/src/lib.rs

@@ -19,7 +19,8 @@ pub use debug_format::{
     AttachRequest, DebugRequest, DebugScenario, DebugTaskFile, LaunchRequest, TcpArgumentsTemplate,
 };
 pub use task_template::{
-    DebugArgsRequest, HideStrategy, RevealStrategy, TaskModal, TaskTemplate, TaskTemplates,
+    DebugArgsRequest, HideStrategy, RevealStrategy, TaskTemplate, TaskTemplates,
+    substitute_all_template_variables_in_str,
 };
 pub use vscode_debug_format::VsCodeDebugTaskFile;
 pub use vscode_format::VsCodeTaskFile;
@@ -266,6 +267,10 @@ impl TaskVariables {
             }
         })
     }
+
+    pub fn iter(&self) -> impl Iterator<Item = (&VariableName, &String)> {
+        self.0.iter()
+    }
 }
 
 impl FromIterator<(VariableName, String)> for TaskVariables {