fix(ast): handle computed property names in Node.Text

[Zzzen]

fix #2890

[ahejlsberg]

The Node.Text method is intended to just me an accessor for nodes that have a text property. It is not supposed to compute a .String() like representation of the node. I think the fix here is to not call Node.Text in the first place on nodes without a text property.

[jakebailey]

Yeah, don't let the JSDoc bit fool you, that is just a performance optimization we didn't need in JS due to deferred string building meaning it was rarely read.

[jakebailey]

#2892