Fixed normalization for metric tag values

[jamescrosswell]

Resolves #3261

See:

• Metric normalization #3271 (comment)

[bruno-garcia]

too bad we can't use char here instead of strings.

Everything on the left is char though, could it be

new KeyValuePair<char, string>('\n', @"\r"),

prob on the right too actually

[jamescrosswell]

The first three replacements are replacing a single control character with a string of length 2 (so '/r' gets replaced with @"/r", for example).

So yes, potentially we could store the LazyTagValueReplacements as a list of KVP<char, string> but there's no overload of String.Replace that takes char as the first argument and string as the second... so we'd need to do an unecessary conversion every time the method was called, in that case... which doesn't seem very efficient.

I figured I'd use the types that were going to be used by method that makes use of them then.