[Trimming] Remove unnecessary regular expressions (#21497)

* Remove unused usign in Routing

* Remove regex for checking x:Class in XamlLoader

* Remove simple regex from KeyboardAutoManagerScroll in iOS

* Remove simple regex from PathBuilder

src/Controls/src/Core/Routing.cs

@@ -3,7 +3,6 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
-using System.Text.RegularExpressions;
 
 namespace Microsoft.Maui.Controls
 {

src/Controls/src/Xaml/XamlLoader.cs

@@ -32,7 +32,6 @@
 using System.IO;
 using System.Linq;
 using System.Reflection;
-using System.Text.RegularExpressions;
 using System.Xml;
 using Microsoft.Maui.Controls.Internals;
 using Microsoft.Maui.Controls.Xaml.Diagnostics;
@@ -355,12 +354,85 @@ static string ReadResourceAsXaml(Type type, Assembly assembly, string likelyTarg
 
 				var xaml = reader.ReadToEnd();
 
-				var pattern = $"x:Class *= *\"{type.FullName}\"";
-				var regex = new Regex(pattern, RegexOptions.ECMAScript);
-				if (regex.IsMatch(xaml) || xaml.IndexOf($"x:Class=\"{type.FullName}\"") != -1)
+				if (ContainsXClass(xaml, type.FullName))
+				{
 					return xaml;
+				}
 			}
 			return null;
+
+			// Equivalent to regex $"x:Class *= *\"{fullName}\""
+			static bool ContainsXClass(string xaml, string fullName)
+			{
+				int index = 0;
+				while (index >= 0 && index < xaml.Length)
+				{
+					if (FindNextXClass()
+						&& SkipWhitespaces()
+						&& NextCharacter('=')
+						&& SkipWhitespaces()
+						&& NextCharacter('"')
+						&& NextFullName()
+						&& NextCharacter('"'))
+					{
+						return true;
+					}
+				}
+
+				return false;
+
+				bool FindNextXClass()
+				{
+					const string xClass = "x:Class";
+
+					index = xaml.IndexOf(xClass, startIndex: index);
+					if (index < 0)
+					{
+						return false;
+					}
+
+					index += xClass.Length;
+					return true;
+				}
+
+				bool SkipWhitespaces()
+				{
+					while (index < xaml.Length && xaml[index] == ' ')
+					{
+						index++;
+					}
+
+					return true;
+				}
+
+				bool NextCharacter(char character)
+				{
+					if (index < xaml.Length && xaml[index] != character)
+					{
+						return false;
+					}
+
+					index++;
+					return true;
+				}
+
+				bool NextFullName()
+				{
+					if (index >= xaml.Length - fullName.Length)
+					{
+						return false;
+					}
+
+					var slice = xaml.AsSpan().Slice(index, fullName.Length);
+					if (!MemoryExtensions.Equals(slice, fullName.AsSpan(), StringComparison.Ordinal))
+					{
+						return false;
+					}
+
+					index += fullName.Length;
+					return true;
+				}
+			}
 		}
 	}
 }

src/Core/src/Platform/iOS/KeyboardAutoManagerScroll.cs

@@ -6,7 +6,7 @@
  */
 
 using System;
-using System.Text.RegularExpressions;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using CoreGraphics;
@@ -254,8 +254,7 @@ static void AnimateHidingKeyboard()
 		if (description is null)
 			return null;
 
-		// remove everything except for numbers and commas
-		var temp = Regex.Replace(description, @"[^0-9,]", "");
+		var temp = RemoveEverythingExceptForNumbersAndCommas(description);
 		var dimensions = temp.Split(',');
 
 		if (dimensions.Length == 4
@@ -268,6 +267,19 @@ static void AnimateHidingKeyboard()
 		}
 
 		return null;
+
+		static string RemoveEverythingExceptForNumbersAndCommas(string input)
+		{
+			var sb = new StringBuilder(input.Length);
+			foreach (var character in input)
+			{
+				if (char.IsDigit(character) || character == ',')
+				{
+					sb.Append(character);
+				}
+			}
+			return sb.ToString();
+		}
 	}
 
 	// Used to debounce calls from different oberservers so we can be sure

src/Graphics/src/Graphics/PathBuilder.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Text;
-using System.Text.RegularExpressions;
 
 namespace Microsoft.Maui.Graphics
 {
@@ -117,7 +116,7 @@ public PathF BuildPath(string pathAsString)
 #else
 				pathAsString = pathAsString.Replace("Infinity", "0", StringComparison.Ordinal);
 #endif
-				pathAsString = Regex.Replace(pathAsString, "([a-zA-Z])", " $1 ");
+				pathAsString = SeparateLetterCharsWithSpaces(pathAsString);
 #if NETSTANDARD2_0
 				pathAsString = pathAsString.Replace("-", " -");
 				pathAsString = pathAsString.Replace(" E  -", "E-");
@@ -214,6 +213,25 @@ public PathF BuildPath(string pathAsString)
 #endif
 			}
 
+			static string SeparateLetterCharsWithSpaces(string input)
+			{
+				var sb = new StringBuilder(input.Length, maxCapacity: 3 * input.Length);
+				foreach (var character in input)
+				{
+					if (char.IsLetter(character))
+					{
+						sb.Append(' ');
+						sb.Append(character);
+						sb.Append(' ');
+					}
+					else
+					{
+						sb.Append(character);
+					}
+				}
+				return sb.ToString();
+			}
+
 			return _path;
 		}