Cache regex instances in most cases (#27699)

Using static Regex functions that take in a pattern is bad because the pattern constantly needs to be re-parsed. With https://github.com/space-wizards/RobustToolbox/pull/5107, the engine has an analyzer to warn for this practice now.

This commit brings most of content up to snuff already, though some of the tricker code I left for somebody else.

Content.Server/Speech/EntitySystems/SouthernAccentSystem.cs

@@ -5,8 +5,12 @@ namespace Content.Server.Speech.EntitySystems;
 
 public sealed class SouthernAccentSystem : EntitySystem
 {
+    private static readonly Regex RegexIng = new(@"ing\b");
+    private static readonly Regex RegexAnd = new(@"\band\b");
+    private static readonly Regex RegexDve = new("d've");
+
     [Dependency] private readonly ReplacementAccentSystem _replacement = default!;
-    
+
     public override void Initialize()
     {
         base.Initialize();
@@ -20,9 +24,9 @@ public sealed class SouthernAccentSystem : EntitySystem
         message = _replacement.ApplyReplacements(message, "southern");
 
         //They shoulda started runnin' an' hidin' from me!
-        message = Regex.Replace(message, @"ing\b", "in'");
-        message = Regex.Replace(message, @"\band\b", "an'");
-        message = Regex.Replace(message, "d've", "da");
+        message = RegexIng.Replace(message, "in'");
+        message = RegexAnd.Replace(message, "an'");
+        message = RegexDve.Replace(message, "da");
         args.Message = message;
     }
 };