Make sure Humanize(LetterCasing.Sentence) does not remove commas (#1185)

- Adapt code so that mid-sentence punctuation is kept when humanizing to a sentence
- Split a regex into simpler constituent parts, easier to reason about
- Add tests

src/Humanizer.Tests.Shared/StringHumanizeTests.cs

@@ -92,6 +92,8 @@ public void CanHumanizeIntoLowerCase(string input, string expectedResult)
         [InlineData("CanReturnSentenceCase", "Can return sentence case")]
         [InlineData("", "")]
         [InlineData("égoïste", "Égoïste")]
+        [InlineData("Normal; Normal and PascalCase", "Normal; normal and pascal case")]
+        [InlineData("I,and No One else", "I, and no one else")]
         public void CanHumanizeIntoSentenceCase(string input, string expectedResult)
         {
             Assert.Equal(expectedResult, input.Humanize(LetterCasing.Sentence));

src/Humanizer/StringHumanizeExtensions.cs

@@ -10,9 +10,16 @@ public static class StringHumanizeExtensions
         private static readonly Regex PascalCaseWordPartsRegex;
         private static readonly Regex FreestandingSpacingCharRegex;
 
+        private const string OptionallyCapitalizedWord = @"\p{Lu}?\p{Ll}+";
+        private const string IntegerAndOptionalLowercaseLetters = @"[0-9]+\p{Ll}*";
+        private const string Acronym = @"\p{Lu}+(?=\p{Lu}|[0-9]|\b)";
+        private const string SequenceOfOtherLetters = @"\p{Lo}+";
+        private const string MidSentencePunctuation = "[,;]?";
+
         static StringHumanizeExtensions()
         {
-            PascalCaseWordPartsRegex = new Regex(@"[\p{Lu}]?[\p{Ll}]+|[0-9]+[\p{Ll}]*|[\p{Lu}]+(?=[\p{Lu}][\p{Ll}]|[0-9]|\b)|[\p{Lo}]+",
+            PascalCaseWordPartsRegex = new Regex(
+                $"({OptionallyCapitalizedWord}|{IntegerAndOptionalLowercaseLetters}|{Acronym}|{SequenceOfOtherLetters}){MidSentencePunctuation}",
                 RegexOptions.IgnorePatternWhitespace | RegexOptions.ExplicitCapture | RegexOptionsUtil.Compiled);
             FreestandingSpacingCharRegex = new Regex(@"\s[-_]|[-_]\s", RegexOptionsUtil.Compiled);
         }