Fixes#2290.

We were scanning into an AST node ingetTokenAtPosition, basically because in this JSDoc case:

/** *@type {{ * 'string-property': boolean; */*$*/identifierProperty:boolean;*}}*/varsomeVariable;

identifierProperty's positiondoes not include what would typically be its leading trivia. So the positions between the starting* andidentifierProperty effectively don't belong to any node or token in the AST, butgetTokenAtPosition operated under the assumption that this was impossible, and therefore that we should scan and find a non-tree token in between* andidentifierProperty.

I added code to explicitly track what the next AST node is (nodeAfterLeft) whenever we update the scanner starting position (left), so we can then enforce the invariant of scanning only in between AST nodes.