Add documentation to many core editor types (#7919)

Hopefully this makes it a bit easier for new contributors to dive into
the codebase :)

Release Notes:

- Improved documentation for many core editor types

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>

crates/editor/src/display_map.rs

@@ -67,15 +67,27 @@ pub trait ToDisplayPoint {
 type TextHighlights = TreeMap<Option<TypeId>, Arc<(HighlightStyle, Vec<Range<Anchor>>)>>;
 type InlayHighlights = BTreeMap<TypeId, HashMap<InlayId, (HighlightStyle, InlayHighlight)>>;
 
+/// Decides how text in a [`MultiBuffer`] should be displayed in a buffer, handling inlay hints,
+/// folding, hard tabs, soft wrapping, custom blocks (like diagnostics), and highlighting.
+///
+/// See the [module level documentation](self) for more information.
 pub struct DisplayMap {
+    /// The buffer that we are displaying.
     buffer: Model<MultiBuffer>,
     buffer_subscription: BufferSubscription,
-    fold_map: FoldMap,
+    /// Decides where the [`Inlay`]s should be displayed.
     inlay_map: InlayMap,
+    /// Decides where the fold indicators should be and tracks parts of a source file that are currently folded.
+    fold_map: FoldMap,
+    /// Keeps track of hard tabs in a buffer.
     tab_map: TabMap,
+    /// Handles soft wrapping.
     wrap_map: Model<WrapMap>,
+    /// Tracks custom blocks such as diagnostics that should be displayed within buffer.
     block_map: BlockMap,
+    /// Regions of text that should be highlighted.
     text_highlights: TextHighlights,
+    /// Regions of inlays that should be highlighted.
     inlay_highlights: InlayHighlights,
     pub clip_at_line_ends: bool,
 }