[RopeModule] Reduce test workload on watchOS

Tests/RopeModuleTests/SampleStrings.swift

@@ -27,7 +27,8 @@ func randomStride(
   })
 }
 
-let sampleString = #"""
+let sampleString: String = {
+  var str = #"""
     The powerful programming language that is also easy to learn.
     Swift is a powerful and intuitive programming language for iOS, iPadOS, macOS, \#
     tvOS, and watchOS. Writing Swift code is interactive and fun, the syntax is \#
@@ -58,10 +59,16 @@ let sampleString = #"""
     ¯\_(ツ)_/¯
     ಠ_ಠ
     
-    🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦\#
+    🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦
+    """#
+  if MemoryLayout<Int>.size == 8 {
+    /// Add even more flags and extra long combining sequences. This considerably increases test
+    /// workload. (Not necessarily due to grapheme cluster length, but because test performance is
+    /// quadratic or worse in the size of the overall text.)
+    str += #"""
     🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦\#
     🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦🇺🇸🇨🇦
-    
+
     Unicode is such fun!
     U̷n̷i̷c̷o̴d̴e̷ ̶i̸s̷ ̸s̵u̵c̸h̷ ̸f̵u̷n̴!̵
     U̴̡̲͋̾n̵̻̳͌ì̶̠̕c̴̭̈͘ǫ̷̯͋̊d̸͖̩̈̈́ḛ̴́ ̴̟͎͐̈i̴̦̓s̴̜̱͘ ̶̲̮̚s̶̙̞͘u̵͕̯̎̽c̵̛͕̜̓h̶̘̍̽ ̸̜̞̿f̵̤̽ṷ̴͇̎͘ń̷͓̒!̷͍̾̚
@@ -70,9 +77,12 @@ let sampleString = #"""
     
     T̸h̴e̶ ̵p̷o̷w̶e̵r̷f̸u̷l̷ ̵p̴r̷o̷g̶r̷a̸m̸m̶i̸n̴g̴ ̷l̶a̴n̸g̵u̵a̶g̸e̶ ̸t̶h̴a̵t̵ ̶i̷s̶ ̵a̷l̴s̸o̷ ̵e̵a̷s̷y̴ ̵t̵o̷ ̷l̷e̶a̵r̴n̸.̵
     """#
+  }
+  return str
+}()
 
 let shortSample = #"""
-    Swift 👨‍👨‍👧‍👧 简洁 c̴̭̈͘ǫ̷̯͋̊d̸͖̩̈̈́ḛ̴́ 🇺🇸🇨🇦🇺🇸 코드
+    Swift 👨‍👨‍👧‍👧简c̴̭̈͘ǫ̷̯͋̊d̸͖̩̈̈́ḛ̴́🇺🇸🇨🇦🇺🇸코
     """#
 
 let sampleString2 =