Perf improvements to char.IsWhiteSpace / char.IsUpper / char.IsLower - #26848

[Benchmark]
[ArgumentsSource(nameof(TrimArguments))]
public ReadOnlySpan<char> Trim(string input) => input.AsSpan().Trim();

[Benchmark]
[Arguments("Hello there, Constable!")]
public int CountLowerChars(string input)
{
    int count = 0;

    foreach (char ch in input)
    {
        if (char.IsLower(ch)) { count++; }
    }

    return count;
}

[Benchmark]
[Arguments("Hello there, Constable!")]
public int CountUpperChars(string input)
{
    int count = 0;

    foreach (char ch in input)
    {
        if (char.IsUpper(ch)) { count++; }
    }

    return count;
}

public static IEnumerable<object> TrimArguments()
{
    yield return "";
    yield return " abcdefg ";
    yield return "abcdefg";
}