Add keyboard shortcut to toggle Markdown rendered/raw view (#16413)
Description
Adds a rebindable keyboard shortcut (default Cmd+E / Ctrl+E) that
toggles a Markdown file between the rendered and raw views, as an
alternative to clicking the Rendered/Raw control in the pane header.

The shortcut is gated by a keymap context
(MarkdownDisplayModeToggle) rather than by filtering inside the action
handler. FileNotebookView and CodeView each add the context only
when the pane shows the Rendered/Raw control, so the binding is not
triggerable anywhere else and the keystroke falls through in
non-Markdown panes.
Both directions are registered under the same binding name and
description (the same pattern as “Save file”), so Settings > Keyboard
shortcuts shows a single “Toggle Markdown rendered/raw view” row and
rebinding it applies to both views.
The CodeView binding is behind #[cfg(feature = "local_fs")],
matching the existing Rendered/Raw control there.
File-type detection is unchanged. CodeView sets the context when its
Rendered/Raw control is present, so the shortcut and the control always
agree.

Linked Issue
Fixes #11786

 The linked issue is labeled ready-to-spec or
ready-to-implement.
 Where appropriate, screenshots or a short video of the
implementation are included below (especially for user-visible or UI
changes).

Testing
New tests:
-
workspace::view::tests::test_markdown_toggle_shortcut_switches_between_raw_and_rendered_panes
dispatches the keystroke through the focused editor and its ancestors,
the way a real key press is routed, and checks the round trip raw →
rendered → raw, and that the keystroke is unhandled in a .rs pane.
-
notebooks::file::tests::test_markdown_toggle_shortcut_only_handled_for_toggleable_files
checks that the rendered pane only handles the shortcut for files that
show the toggle.
-
util::bindings::tests::test_markdown_display_mode_toggle_is_rebound_in_both_directions
checks that rebinding the shortcut applies to both registrations.
-
notebooks::file::tests::test_markdown_toggle_shortcut_follows_jupyter_notebook_rendering_flag
checks that the rendered pane handles the shortcut for an .ipynb file
only when JupyterNotebookRendering is enabled.
The first two fail if the keymap context is not inserted.
./script/presubmit was run in full on the first commit: format,
clippy, clang-format, wgslfmt and shellcheck pass (PSScriptAnalyzer was
skipped, I don’t have PowerShell installed). 12,737 of 12,743 tests
passed. The 6 failures were 5 SSH integration tests that need access to
the GCP test VM, and ui_tests::test_cloud_agent_shell_respawn, which
passed when re-run on its own. After the later commits I re-ran format,
cargo clippy -p warp --all-targets --tests and the related tests, not
the full suite.
Not covered: the .ipynb toggle shares this shortcut behind
JupyterNotebookRendering. It is tested from the rendered pane only.
There is no test that presses the shortcut in a raw .ipynb pane, and I
did not check notebooks manually.

 I have manually tested my changes locally with ./script/run

Screenshots / Videos
https://github.com/user-attachments/assets/11d698c4-a41f-4c5d-ac2f-86dfcc3a9f43
Agent Mode

 Warp Agent Mode - This PR was created via Warp’s AI Agent Mode

CHANGELOG-IMPROVEMENT: Added a keyboard shortcut (Cmd+E / Ctrl+E,
rebindable) to toggle Markdown files between rendered and raw view.
Co-Authored-By: Claude Code