Load all key bindings that parse and use markdown in error notifications (#23113)

* Collects and reports all parse errors

* Shares parsed `KeyBindingContextPredicate` among the actions.

* Updates gpui keybinding and action parsing to return structured
errors.

* Renames "block" to "section" to match the docs, as types like
`KeymapSection` are shown in `json-language-server` hovers.

* Removes wrapping of `context` and `use_key_equivalents` fields so that
`json-language-server` auto-inserts `""` and `false` instead of `null`.

* Updates `add_to_cx` to take `&self`, so that the user keymap doesn't
get unnecessarily cloned.

In retrospect I wish I'd just switched to using TreeSitter to do the
parsing and provide proper diagnostics. This is tracked in #23333

Release Notes:

- Improved handling of errors within the user keymap file. Parse errors
within context, keystrokes, or actions no longer prevent loading the key
bindings that do parse.

crates/markdown_preview/src/markdown_renderer.rs

@@ -110,15 +110,15 @@ pub fn render_parsed_markdown(
     parsed: &ParsedMarkdown,
     workspace: Option<WeakView<Workspace>>,
     cx: &WindowContext,
-) -> Vec<AnyElement> {
+) -> Div {
     let mut cx = RenderContext::new(workspace, cx);
-    let mut elements = Vec::new();
 
-    for child in &parsed.children {
-        elements.push(render_markdown_block(child, &mut cx));
-    }
-
-    elements
+    v_flex().gap_3().children(
+        parsed
+            .children
+            .iter()
+            .map(|block| render_markdown_block(block, &mut cx)),
+    )
 }
 
 pub fn render_markdown_block(block: &ParsedMarkdownElement, cx: &mut RenderContext) -> AnyElement {