Extend generators

[brandonspark]

What: Currently, generators are only limitedly supported. We don't allow newlines between clauses of the comprehension, so things like

(x for z in [1,2] if true)

parse fine, but if you change it to any of the following:

(c
 for x in [1, 2]
 if true
) 
(c
 for x in [1, 2]
 if true)
(c
 for x in [1, 2] if true)
(c
 for x in [1, 2] if true
)

it breaks.

Why: We should do this, because this actually happens.

How: Added some extra optional terminators. These should allow generous use of newlines and semicolons.

I also needed to add precedence to for_clause and if_clause over for_statement and if_statement. This was so generators would not parse as parenthesized expressions containing for statements, and related.

[savq]

This fails for me on some basic expressions:

# generators.jl
(x for x in xs)

tree-sitter parse generators.jl # master

``` (source_file [0, 0] - [3, 0] (line_comment [0, 0] - [0, 15]) (generator_expression [1, 0] - [1, 15] (identifier [1, 1] - [1, 2]) (for_clause [1, 3] - [1, 14] (for_binding [1, 7] - [1, 14] (identifier [1, 7] - [1, 8]) (identifier [1, 12] - [1, 14]))))) ```

tree-sitter parse generators.jl # brandonspark:extend-generators

``` (source_file [0, 0] - [3, 0] (line_comment [0, 0] - [0, 15]) (parenthesized_expression [1, 0] - [1, 15] (identifier [1, 1] - [1, 2]) (ERROR [1, 3] - [1, 14] (for_clause [1, 3] - [1, 14] (for_binding [1, 7] - [1, 14] (identifier [1, 7] - [1, 8]) (identifier [1, 12] - [1, 14])))))) ```

Works again if you add an if_clause:

# generators.jl
(x for x in xs if x != missing)

tree-sitter parse generators.jl # brandonspark:extend-generators

``` (source_file [0, 0] - [3, 0] (line_comment [0, 0] - [0, 15]) (generator_expression [1, 0] - [1, 31] (identifier [1, 1] - [1, 2]) (for_clause [1, 3] - [1, 14] (for_binding [1, 7] - [1, 14] (identifier [1, 7] - [1, 8]) (identifier [1, 12] - [1, 14]))) (if_clause [1, 15] - [1, 30] (binary_expression [1, 18] - [1, 30] (identifier [1, 18] - [1, 19]) (operator [1, 20] - [1, 22]) (identifier [1, 23] - [1, 30]))))) ```

We probably need tests without if clauses.

[maxbrunsfeld]

Nice, thanks for catching that @savq.