fix(iOS): apply zero width space for headings (#597)

# Summary

This PR: 

- apply zero width space for headings
- adds `applyStylingToTypingAttrs` method in `StyleBase` to properly
align cursor styles on empty line

## Test Plan

Play around with headings, and check If the style work properly, cursor
is properly styled.

## Screenshots / Videos
Before:


https://github.com/user-attachments/assets/965e8d58-21dc-4f0e-a9b4-8c8ea69084dd


After:


https://github.com/user-attachments/assets/97b5ee50-5fc5-4908-b5ad-dff5858cb10c


## Compatibility

| OS      | Implemented |
| ------- | :---------: |
| iOS     |    ✅     |
| Android |    ❌     |

## Checklist

- [x] E2E tests are passing
- [ ] Required E2E tests have been added (if applicable)

---------

Author: kacperzolkiewski

.maestro/enrichedInput/flows/conflicting_paragraph_merge.yaml

@@ -28,8 +28,6 @@ appId: swmansion.enriched.example
 - pressKey: Backspace
 
 - runFlow:
-    when:
-        platform: "android"
     commands:
         - pressKey: Backspace
 - inputText: " "

ios/inputAttributesManager/InputAttributesManager.mm

@@ -192,6 +192,15 @@ - (void)manageTypingAttributesWithOnlySelection:(BOOL)onlySelectionChanged {
     newAttrs[entry.key] = entry.value;
   }
 
+  // Apply active styles to typing attributes only for styles that require it so
+  // the cursor correctly reflects the current formatting state (e.g. heading
+  // size).
+  for (StyleBase *style in _input->stylesDict.allValues) {
+    if ([style appliesStylingToTyping] && [style detect:selectedRange]) {
+      [style applyStylingToTypingAttrs:newAttrs];
+    }
+  }
+
   textView.typingAttributes = newAttrs;
 }
 

ios/interfaces/StyleBase.h

@@ -12,6 +12,7 @@
 - (NSString *)getValue;
 - (BOOL)isParagraph;
 - (BOOL)needsZWS;
+- (BOOL)appliesStylingToTyping;
 - (instancetype)initWithHost:(id<EnrichedViewHost>)host;
 - (NSRange)actualUsedRange:(NSRange)range;
 - (void)toggle:(NSRange)range;
@@ -30,6 +31,7 @@
 - (BOOL)any:(NSRange)range;
 - (NSArray<StylePair *> *)all:(NSRange)range;
 - (void)applyStyling:(NSRange)range;
+- (void)applyStylingToTypingAttrs:(NSMutableDictionary *)attributes;
 - (void)reapplyFromStylePair:(StylePair *)pair;
 - (AttributeEntry *)getEntryIfPresent:(NSRange)range;
 @end

ios/interfaces/StyleBase.mm

@@ -34,6 +34,10 @@ - (BOOL)needsZWS {
   return NO;
 }
 
+- (BOOL)appliesStylingToTyping {
+  return NO;
+}
+
 - (instancetype)initWithHost:(id<EnrichedViewHost>)host {
   self = [super init];
   _host = host;
@@ -232,6 +236,11 @@ - (BOOL)any:(NSRange)range {
 - (void)applyStyling:(NSRange)range {
 }
 
+// This method gets overridden when the style needs to apply certain typing
+// attributes
+- (void)applyStylingToTypingAttrs:(NSMutableDictionary *)attributes {
+}
+
 // Called during dirty range re-application to restore a style from a saved
 // StylePair
 - (void)reapplyFromStylePair:(StylePair *)pair {

ios/styles/HeadingStyleBase.mm

@@ -22,6 +22,14 @@ - (BOOL)isParagraph {
   return YES;
 }
 
+- (BOOL)needsZWS {
+  return YES;
+}
+
+- (BOOL)appliesStylingToTyping {
+  return YES;
+}
+
 - (void)applyStyling:(NSRange)range {
   [self.host.textView.textStorage
       enumerateAttribute:NSFontAttributeName
@@ -42,12 +50,36 @@ - (void)applyStyling:(NSRange)range {
               }];
 }
 
+- (void)applyStylingToTypingAttrs:(NSMutableDictionary *)attributes {
+  UIFont *currentFont = attributes[NSFontAttributeName];
+
+  if (currentFont == nil) {
+    currentFont = [self.host.config primaryFont];
+  }
+
+  UIFont *newFont = [currentFont setSize:[self getHeadingFontSize]];
+  if ([self isHeadingBold]) {
+    newFont = [newFont setBold];
+  }
+
+  attributes[NSFontAttributeName] = newFont;
+}
+
 // used to make sure headings dont persist after a newline is placed
 - (BOOL)handleNewlinesInRange:(NSRange)range replacementText:(NSString *)text {
   // in a heading and a new text ends with a newline
   if ([self detect:self.host.textView.selectedRange] && text.length > 0 &&
       [[NSCharacterSet newlineCharacterSet]
           characterIsMember:[text characterAtIndex:text.length - 1]]) {
+    // If the cursor sits directly before a ZWS, skip past it so the newline
+    // is appended after the ZWS. This keeps the ZWS (and the heading) on the
+    // current line while the new line the cursor lands on has no heading.
+    // Without this the lone '\n' inherits heading attributes
+    NSString *string = self.host.textView.textStorage.string;
+    if (range.length == 0 && range.location < string.length &&
+        [string characterAtIndex:range.location] == 0x200B) {
+      range = NSMakeRange(range.location + 1, 0);
+    }
     // do the replacement manually
     [TextInsertionUtils replaceText:text
                                  at:range