git: Handle shift-click to stage a range of entries in the panel (#34296)

Release Notes:

- git: shift-click can now be used to stage a range of entries in the
git panel.

assets/keymaps/default-linux.json

@@ -856,6 +856,7 @@
       "alt-shift-y": "git::UnstageFile",
       "ctrl-alt-y": "git::ToggleStaged",
       "space": "git::ToggleStaged",
+      "shift-space": "git::StageRange",
       "tab": "git_panel::FocusEditor",
       "shift-tab": "git_panel::FocusEditor",
       "escape": "git_panel::ToggleFocus",

assets/keymaps/default-macos.json

@@ -930,6 +930,7 @@
       "enter": "menu::Confirm",
       "cmd-alt-y": "git::ToggleStaged",
       "space": "git::ToggleStaged",
+      "shift-space": "git::StageRange",
       "cmd-y": "git::StageFile",
       "cmd-shift-y": "git::UnstageFile",
       "alt-down": "git_panel::FocusEditor",

assets/keymaps/vim.json

@@ -841,6 +841,7 @@
       "i": "git_panel::FocusEditor",
       "x": "git::ToggleStaged",
       "shift-x": "git::StageAll",
+      "g x": "git::StageRange",
       "shift-u": "git::UnstageAll"
     }
   },