Use StartsWith(char value) for modern TFM

Author: jnyrup

Src/FluentAssertions/CallerIdentifier.cs

@@ -243,7 +243,7 @@ private static bool StartsWithNewKeyword(string candidate)
 
     private static bool IsStringLiteral(string candidate)
     {
-        return candidate.StartsWith("\"", StringComparison.Ordinal);
+        return candidate.StartsWith('\"');
     }
 
     private static bool IsNumeric(string candidate)

Src/FluentAssertions/Common/StringExtensions.cs

@@ -88,7 +88,7 @@ public static string Combine(this string @this, string other, string separator =
             return @this;
         }
 
-        if (other.StartsWith("[", StringComparison.Ordinal))
+        if (other.StartsWith('['))
         {
             separator = string.Empty;
         }

Src/FluentAssertions/SystemExtensions.cs

@@ -16,4 +16,8 @@ public static bool Contains(this string str, string value, StringComparison comp
 
     public static bool Contains(this string str, char value, StringComparison comparison) =>
         str.IndexOf(value, comparison) != -1;
+
+    // https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs,1014
+    public static bool StartsWith(this string str, char value) =>
+        str.Length != 0 && str[0] == value;
 }