ordering of parsing statements variants

[OmarTawfik]

We should look into this once #808 is ready:

I see ExpressionStatement and VariableDeclarationStatement were moved to the top. Is it just for organization, or does it impact parsing?

I'm asking because almost all other variants start with a unique token, so it should be faster to parse/validate them, instead of trying to parse a full expression, then backtracking when it fails.

Originally posted by @OmarTawfik in #653 (comment)