Headings on markdown preset use different sizes (#59)

* Headings increase in size

* Fixes insertion point graphical glitches

* Updates markdown preset snapshots for large headings

* Updates markdown preset snapshots for large headings in AppKit

Author: kyle-n

Sources/HighlightedTextEditor/HighlightedTextEditor.AppKit.swift

@@ -54,6 +54,7 @@ public struct HighlightedTextEditor: NSViewRepresentable, HighlightingTextEditor
 
     public func updateNSView(_ view: ScrollableTextView, context: Context) {
         context.coordinator.updatingNSView = true
+        let typingAttributes = view.textView.typingAttributes
 
         let highlightedText = HighlightedTextEditor.getHighlightedText(
             text: text,
@@ -63,6 +64,7 @@ public struct HighlightedTextEditor: NSViewRepresentable, HighlightingTextEditor
         view.attributedText = highlightedText
         runIntrospect(view)
         view.selectedRanges = context.coordinator.selectedRanges
+        view.textView.typingAttributes = typingAttributes
         context.coordinator.updatingNSView = false
     }
 

Sources/HighlightedTextEditor/Presets/Markdown.swift

@@ -53,14 +53,22 @@ let lighterColor = UIColor.lightGray
 let textColor = UIColor.label
 #endif
 
+private let maxHeadingLevel = 6
+
 public extension Sequence where Iterator.Element == HighlightRule {
     static var markdown: [HighlightRule] {
         [
             HighlightRule(pattern: inlineCodeRegex, formattingRule: TextFormattingRule(key: .font, value: codeFont)),
             HighlightRule(pattern: codeBlockRegex, formattingRule: TextFormattingRule(key: .font, value: codeFont)),
             HighlightRule(pattern: headingRegex, formattingRules: [
                 TextFormattingRule(fontTraits: headingTraits),
-                TextFormattingRule(key: .kern, value: 0.5)
+                TextFormattingRule(key: .kern, value: 0.5),
+                TextFormattingRule(key: .font, calculateValue: { content, _ in
+                    let uncappedLevel = content.prefix(while: { char in char == "#" }).count
+                    let level = Swift.min(maxHeadingLevel, uncappedLevel)
+                    let fontSize = CGFloat(maxHeadingLevel - level) * 2.5 + defaultEditorFont.pointSize
+                    return SystemFontAlias(descriptor: defaultEditorFont.fontDescriptor, size: fontSize) as Any
+                })
             ]),
             HighlightRule(
                 pattern: linkOrImageRegex,