fix: handling of zero-width space (ZWS) offset inside parser (#500)

# Summary

Fixes: #419 

This PR fixes handling of zero-width space (ZWS) offset inside empty
paragraphs, ensuring parsed styles are applied in correct position in
`applyProcessedStyles`.

## Test Plan

1. Run test case from the issue: #419 
2. Insert some other `html` examples by "Set Input's value' button in
example app and check if they are displayed properly

## Screenshots / Videos


https://github.com/user-attachments/assets/6c1aaad4-6b02-45b8-8422-3039b14ac6a3



## Compatibility

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

## Checklist

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

Author: kacperzolkiewski

ios/inputParser/InputParser.mm

@@ -677,22 +677,34 @@ - (void)insertFromHtml:(NSString *_Nonnull)html location:(NSInteger)location {
 - (void)applyProcessedStyles:(NSArray *)processedStyles
          offsetFromBeginning:(NSInteger)offset
              plainTextLength:(NSUInteger)plainTextLength {
+  // Some paragraph styles (codeblock, blockquote, etc.) insert \u200B
+  // into empty lines, mutating NSTextStorage length. We need to
+  // shift subsequent ranges by this offset.
+  NSInteger zeroWidthSpaceOffset = 0;
+
   for (NSArray *arr in processedStyles) {
     // unwrap all info from processed style
     NSNumber *styleType = (NSNumber *)arr[0];
     StylePair *stylePair = (StylePair *)arr[1];
     StyleBase *baseStyle = _input->stylesDict[styleType];
-    // range must be taking offest into consideration because processed styles'
-    // ranges are relative to only the new text while we need absolute ranges
-    // relative to the whole existing text
+    NSRange parsedRange = [stylePair.rangeValue rangeValue];
+    NSUInteger textLengthBeforeStyleApplied =
+        _input->textView.textStorage.string.length;
+    // range must be taking zeroWidthSpaceOffset and offest into consideration
+    // because processed styles ranges are relative to only the new text while
+    // we need absolute ranges relative to the whole existing text
     NSRange styleRange =
-        NSMakeRange(offset + [stylePair.rangeValue rangeValue].location,
-                    [stylePair.rangeValue rangeValue].length);
+        NSMakeRange(offset + zeroWidthSpaceOffset + parsedRange.location,
+                    parsedRange.length);
 
     // of course any changes here need to take blocks and conflicts into
     // consideration
     if ([_input handleStyleBlocksAndConflicts:[[baseStyle class] getType]
                                         range:styleRange]) {
+      BOOL shouldAddTypingAttr =
+          styleRange.location + styleRange.length ==
+          plainTextLength + offset + zeroWidthSpaceOffset;
+
       if ([styleType isEqualToNumber:@([LinkStyle getType])]) {
         LinkData *linkData = (LinkData *)stylePair.styleValue;
         [((LinkStyle *)baseStyle) addLink:linkData
@@ -713,32 +725,36 @@ - (void)applyProcessedStyles:(NSArray *)processedStyles
 
         // First apply the checkbox list style to the entire range with
         // unchecked value
-        BOOL shouldAddTypingAttr =
-            styleRange.location + styleRange.length == plainTextLength;
         [cbLStyle addWithChecked:NO
                            range:styleRange
                       withTyping:shouldAddTypingAttr
                   withDirtyRange:YES];
 
-        if (!checkboxStates && checkboxStates.count == 0) {
-          continue;
-        }
-        // Then toggle checked checkboxes
-        for (NSNumber *key in checkboxStates) {
-          NSUInteger checkboxPosition = offset + [key unsignedIntegerValue];
-          BOOL isChecked = [checkboxStates[key] boolValue];
-          if (isChecked) {
-            [cbLStyle toggleCheckedAt:checkboxPosition];
+        if (checkboxStates && checkboxStates.count > 0) {
+          // Then toggle checked checkboxes
+          for (NSNumber *key in checkboxStates) {
+            NSUInteger checkboxPosition =
+                offset + zeroWidthSpaceOffset + [key unsignedIntegerValue];
+            BOOL isChecked = [checkboxStates[key] boolValue];
+            if (isChecked) {
+              [cbLStyle toggleCheckedAt:checkboxPosition];
+            }
           }
         }
       } else {
-        BOOL shouldAddTypingAttr =
-            styleRange.location + styleRange.length == plainTextLength;
         [baseStyle add:styleRange
                 withTyping:shouldAddTypingAttr
             withDirtyRange:YES];
       }
     }
+
+    NSInteger delta = (NSInteger)_input->textView.textStorage.string.length -
+                      (NSInteger)textLengthBeforeStyleApplied;
+    // Image shifts are already handled by _precedingImageCount during tag
+    // finalization.
+    if (delta != 0 && ![styleType isEqualToNumber:@([ImageStyle getType])]) {
+      zeroWidthSpaceOffset += delta;
+    }
   }
   [_input anyTextMayHaveBeenModified];
 }