toolchains: Allow users to provide custom paths to toolchains (#37009)

- **toolchains: Add new state to toolchain selector**
- **Use toolchain term for Add Toolchain button**
- **Hoist out a meta function for toolchain listers**

Closes #27332

Release Notes:

- python: Users can now specify a custom path to their virtual
environment from within the picker.

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

assets/keymaps/default-linux.json

@@ -628,6 +628,7 @@
       "alt-save": "workspace::SaveAll",
       "ctrl-alt-s": "workspace::SaveAll",
       "ctrl-k m": "language_selector::Toggle",
+      "ctrl-k ctrl-m": "toolchain::AddToolchain",
       "escape": "workspace::Unfollow",
       "ctrl-k ctrl-left": "workspace::ActivatePaneLeft",
       "ctrl-k ctrl-right": "workspace::ActivatePaneRight",
@@ -1028,6 +1029,13 @@
       "tab": "channel_modal::ToggleMode"
     }
   },
+  {
+    "context": "ToolchainSelector",
+    "use_key_equivalents": true,
+    "bindings": {
+      "ctrl-shift-a": "toolchain::AddToolchain"
+    }
+  },
   {
     "context": "FileFinder || (FileFinder > Picker > Editor)",
     "bindings": {