debugger: Add keyboard navigation for breakpoint list (#31221)

Release Notes:

- Debugger Beta: made it possible to navigate the breakpoint list using
menu keybindings.

assets/keymaps/default-linux.json

@@ -872,6 +872,13 @@
       "ctrl-i": "debugger::ToggleSessionPicker"
     }
   },
+  {
+    "context": "BreakpointList",
+    "bindings": {
+      "space": "debugger::ToggleEnableBreakpoint",
+      "backspace": "debugger::UnsetBreakpoint"
+    }
+  },
   {
     "context": "CollabPanel && not_editing",
     "bindings": {

assets/keymaps/default-macos.json

@@ -932,6 +932,13 @@
       "cmd-i": "debugger::ToggleSessionPicker"
     }
   },
+  {
+    "context": "BreakpointList",
+    "bindings": {
+      "space": "debugger::ToggleEnableBreakpoint",
+      "backspace": "debugger::UnsetBreakpoint"
+    }
+  },
   {
     "context": "CollabPanel && not_editing",
     "use_key_equivalents": true,