Add unit tests for natural text alignment on iOS

RCTNSTextAttributesFromTextAttributes resolves a paragraph that declares
no textAlign to the start edge of its layout direction, left to right as
well as right to left (#57634, #59249), and leaves it to UIKit when the
text attributes carry no layout direction, as a text input's do.

Cover the three cases. The left-to-right one fails without #59249, where
the paragraph gets no paragraph style at all: a test that read only the
alignment would pass there, since a nil paragraph style reads as
NSTextAlignmentLeft.

Author: YevheniiKotyrlo

packages/react-native/React/Tests/Text/RCTAttributedTextUtilsTest.mm

@@ -43,6 +43,15 @@ static NSTextAlignment NSTextAlignmentFromTextAlign(NSString *textAlign, LayoutD
   return paragraphStyle.alignment;
 }
 
+static NSParagraphStyle *ParagraphStyleFromLayoutDirection(std::optional<LayoutDirection> layoutDirection)
+{
+  TextAttributes textAttributes;
+  textAttributes.layoutDirection = layoutDirection;
+
+  NSDictionary<NSAttributedStringKey, id> *attributes = RCTNSTextAttributesFromTextAttributes(textAttributes);
+  return attributes[NSParagraphStyleAttributeName];
+}
+
 static UIFont *FontFromSettings(std::optional<std::string> settings, std::optional<FontWeight> weight = std::nullopt)
 {
   TextAttributes textAttributes;
@@ -133,6 +142,22 @@ - (void)testTextAlignmentStartAndEndResolveWithLayoutDirection
   XCTAssertEqual(NSTextAlignmentFromTextAlign(@"end", LayoutDirection::RightToLeft), NSTextAlignmentLeft);
 }
 
+- (void)testUndeclaredTextAlignmentResolvesWithLayoutDirection
+{
+  NSParagraphStyle *leftToRight = ParagraphStyleFromLayoutDirection(LayoutDirection::LeftToRight);
+  XCTAssertNotNil(leftToRight);
+  XCTAssertEqual(leftToRight.alignment, NSTextAlignmentLeft);
+
+  NSParagraphStyle *rightToLeft = ParagraphStyleFromLayoutDirection(LayoutDirection::RightToLeft);
+  XCTAssertNotNil(rightToLeft);
+  XCTAssertEqual(rightToLeft.alignment, NSTextAlignmentRight);
+}
+
+- (void)testUndeclaredTextAlignmentWithoutLayoutDirectionStaysNatural
+{
+  XCTAssertNil(ParagraphStyleFromLayoutDirection(std::nullopt));
+}
+
 - (void)testSamenessOfEmptyAttributedStrings
 {
   NSAttributedString *attributedString1 = [[NSAttributedString alloc] initWithString:@""];