debugger: Add an action to rerun the last session (#31442)

This works the same as selecting the first history match in the new
session modal.

Release Notes:

- Debugger Beta: Added the `debugger: rerun last session` action, bound
by default to `alt-f4`.

assets/keymaps/default-linux.json

@@ -31,6 +31,7 @@
       "ctrl-,": "zed::OpenSettings",
       "ctrl-q": "zed::Quit",
       "f4": "debugger::Start",
+      "alt-f4": "debugger::RerunLastSession",
       "f5": "debugger::Continue",
       "shift-f5": "debugger::Stop",
       "ctrl-shift-f5": "debugger::Restart",

assets/keymaps/default-macos.json

@@ -4,6 +4,7 @@
     "use_key_equivalents": true,
     "bindings": {
       "f4": "debugger::Start",
+      "alt-f4": "debugger::RerunLastSession",
       "f5": "debugger::Continue",
       "shift-f5": "debugger::Stop",
       "shift-cmd-f5": "debugger::Restart",