Intern short (1..2 chars) contents of TextNode; Statically preallocate Comma TextNode as mostly used

[SergeiPavlov]

Most typical TextNode is comma+space
Cached queries may contain Megabytes of them:

[alex-kulakov]

I'm going to change target branch to the 7.1 one, it's the version where reworked ContainerNode was introduced sounds reasonable to improve it there

[alex-kulakov]

Static TextNode.Create(string ) methods, as all static methods should be before any instance methods.
So the order should be

1. public readonly string Test;
2. public static TextNode Create(string text) ...
3. internal override void AcceptVisitor(NodeVisitor vistor)

[SergeiPavlov]

Static TextNode.Create(string ) methods, as all static methods should be before any instance methods.

done