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/block_map.rs

@@ -22,6 +22,9 @@ use text::Edit;
 
 const NEWLINES: &[u8] = &[b'\n'; u8::MAX as usize];
 
+/// Tracks custom blocks such as diagnostics that should be displayed within buffer.
+///
+/// See the [`display_map` module documentation](crate::display_map) for more information.
 pub struct BlockMap {
     next_block_id: AtomicUsize,
     wrap_snapshot: RefCell<WrapSnapshot>,

crates/editor/src/display_map/fold_map.rs

@@ -178,6 +178,9 @@ impl<'a> FoldMapWriter<'a> {
     }
 }
 
+/// Decides where the fold indicators should be; also tracks parts of a source file that are currently folded.
+///
+/// See the [`display_map` module documentation](crate::display_map) for more information.
 pub(crate) struct FoldMap {
     snapshot: FoldSnapshot,
     ellipses_color: Option<Hsla>,

crates/editor/src/display_map/inlay_map.rs

@@ -16,6 +16,9 @@ use text::{Patch, Rope};
 
 use super::Highlights;
 
+/// Decides where the [`Inlay`]s should be displayed.
+///
+/// See the [`display_map` module documentation](crate::display_map) for more information.
 pub struct InlayMap {
     snapshot: InlaySnapshot,
     inlays: Vec<Inlay>,

crates/editor/src/display_map/tab_map.rs

@@ -9,6 +9,9 @@ use sum_tree::Bias;
 
 const MAX_EXPANSION_COLUMN: u32 = 256;
 
+/// Keeps track of hard tabs in a text buffer.
+///
+/// See the [`display_map` module documentation](crate::display_map) for more information.
 pub struct TabMap(TabSnapshot);
 
 impl TabMap {

crates/editor/src/display_map/wrap_map.rs

@@ -15,6 +15,9 @@ use text::Patch;
 pub use super::tab_map::TextSummary;
 pub type WrapEdit = text::Edit<u32>;
 
+/// Handles soft wrapping of text.
+///
+/// See the [`display_map` module documentation](crate::display_map) for more information.
 pub struct WrapMap {
     snapshot: WrapSnapshot,
     pending_edits: VecDeque<(TabSnapshot, Vec<TabEdit>)>,