Add git: open modified files action (#32347)

Ported over a vscode/cursor command that I like using : )

Release Notes:

- Added "open modified files" command

assets/keymaps/default-linux.json

@@ -115,6 +115,7 @@
       "ctrl-\"": "editor::ExpandAllDiffHunks",
       "ctrl-i": "editor::ShowSignatureHelp",
       "alt-g b": "git::Blame",
+      "alt-g m": "git::OpenModifiedFiles",
       "menu": "editor::OpenContextMenu",
       "shift-f10": "editor::OpenContextMenu",
       "ctrl-shift-e": "editor::ToggleEditPrediction",

assets/keymaps/default-macos.json

@@ -139,6 +139,7 @@
       "cmd-'": "editor::ToggleSelectedDiffHunks",
       "cmd-\"": "editor::ExpandAllDiffHunks",
       "cmd-alt-g b": "git::Blame",
+      "cmd-alt-g m": "git::OpenModifiedFiles",
       "cmd-i": "editor::ShowSignatureHelp",
       "f9": "editor::ToggleBreakpoint",
       "shift-f9": "editor::EditLogBreakpoint",