Increase the context in other multibuffers (#10582)

This moves the diagnostics and find all references to be in line with
the search pane. This also centralizes the constant into the editor code
base.

Release Notes:

- Increased diagnostic context to match the project search context.

crates/search/src/project_search.rs

@@ -54,8 +54,6 @@ struct ActiveSettings(HashMap<WeakModel<Project>, ProjectSearchSettings>);
 
 impl Global for ActiveSettings {}
 
-const SEARCH_CONTEXT: u32 = 2;
-
 pub fn init(cx: &mut AppContext) {
     cx.set_global(ActiveSettings::default());
     cx.observe_new_views(|workspace: &mut Workspace, _cx| {
@@ -234,7 +232,7 @@ impl ProjectSearch {
                                     excerpts.stream_excerpts_with_context_lines(
                                         buffer,
                                         ranges,
-                                        SEARCH_CONTEXT,
+                                        editor::DEFAULT_MULTIBUFFER_CONTEXT,
                                         cx,
                                     )
                                 })