editor: Use a default font for the minimap (#45999)

Closes #45496
Should help #43460
And probably also #44503

The minimap usually renders about 10x more lines of code and shaped text
than the editor. With expensive fonts such as Google Sans Code, this can
cause noticeable lag, since we attempt to synthesize 300+ lines of code
using a heavy font. Because minimap text is rendered at around 2px and
is essentially illegible, it doesn’t make sense to use the custom buffer
font.

Release Notes:

- Improved minimap performance when using custom fonts

---------

Signed-off-by: Marco Mihai Condrache <52580954+marcocondrache@users.noreply.github.com>

crates/editor/src/editor.rs

@@ -20275,6 +20275,7 @@ impl Editor {
         cx: &mut Context<Self>,
     ) -> Entity<Self> {
         const MINIMAP_FONT_WEIGHT: gpui::FontWeight = gpui::FontWeight::BLACK;
+        const MINIMAP_FONT_FAMILY: SharedString = SharedString::new_static(".ZedMono");
 
         let mut minimap = Editor::new_internal(
             EditorMode::Minimap {
@@ -20290,6 +20291,7 @@ impl Editor {
         minimap.set_text_style_refinement(TextStyleRefinement {
             font_size: Some(MINIMAP_FONT_SIZE),
             font_weight: Some(MINIMAP_FONT_WEIGHT),
+            font_family: Some(MINIMAP_FONT_FAMILY),
             ..Default::default()
         });
         minimap.update_minimap_configuration(minimap_settings, cx);