feat: Hoist preprocessor directives out of statements and expressions

[iwoplaza]

This PR adds a few changes:

• Instead of passing around an array of tokens in the parser, it's now a Tokens object with a cursor. This change was motivated by a comment suggesting this change, as well as the need for a way to signal if a parsed statement contained a directive.
• When parsing, in-statement preprocessor directives are ignored, and the encounteredMacro flag is set to true. If this flag is on after a statement is parsed, the tokens are rearranged, and the resulting tokens are reparsed as a set of statements.