Support tokenize span using more than 1 separator

### Overview

Sometimes a [ReadOnly]Span needs to be tokenized using more than one separator.

### API breakdown

```csharp
namespace CommunityToolkit.HighPerformance;

public static class SpanExtensions
{
public static SpanTokenizer2 Tokenize(this Span span, T separator0, T separator1);
public static SpanTokenizer3 Tokenize(this Span span, T separator0, T separator1, T separator2);
public static SpanTokenizerAny Tokenize(this Span span, ReadOnlySpan separators)
}
```

```csharp
namespace CommunityToolkit.HighPerformance;

public static class ReadOnlySpanExtensions
{
public static ReadOnlySpanTokenizer2 Tokenize(this ReadOnlySpan span, T separator0, T separator1);
public static ReadOnlySpanTokenizer3 Tokenize(this ReadOnlySpan span, T separator0, T separator1, T separator2);
public static ReadOnlySpanTokenizerAny Tokenize(this ReadOnlySpan span, ReadOnlySpan separators)
}
```

### Usage example

```csharp
ReadOnlySpan content = "John; 1960, USA";

foreach (var token in content.Tokenize(';', ',')
{
Console.WriteLine(token.ToString());
}
```

### Breaking change?

No

### Alternatives

Not that I'm aware of.

### Additional context

The new tokenizer structs can use `IndexOfAny` instead of `IndexOf`.

### Help us help you

Yes, I'd like to be assigned to work on this item