Remove newline token

We don't want the newline token to show in the AST as it would make our
passes sensible to that specific token. For instance if the source was

```fortran
\#ifdef HAVE_THING
  ! foo
\#endif
```

we wouldn't want to visit the newline character and make our column
limit algorithm split the `#ifdef` as

```fortran
\#ifdef HAVE_THING \

  ! foo
\#endif
```

In other words, this commit is hidding the newline character in the AST.

Author: inaki-amatria

grammar.js

@@ -100,8 +100,9 @@ module.exports = grammar({
     [$.rank_statement],
     [$.stop_statement, $.identifier],
     [$.type_statement],
-    [$.preproc_ifdef_in_specification_part, $.program],
     [$.preproc_else_in_specification_part, $.program],
+    [$.preproc_if_in_specification_part, $.program],
+    [$._preproc_expression, $._expression],
     [$.coarray_critical_statement, $.identifier],
   ],
 
@@ -2352,7 +2353,6 @@ function preprocIf(suffix, content, precedence = 0) {
       preprocessor('if'),
       field('condition', $._preproc_expression),
       optional($.preproc_comment),
-      '\n',
       field('content', content($)),
       field('alternative', optional(alternativeBlock($))),
       preprocessor('endif'),
@@ -2379,7 +2379,6 @@ function preprocIf(suffix, content, precedence = 0) {
       preprocessor('elif'),
       optional($.preproc_comment),
       field('condition', $._preproc_expression),
-      '\n',
       field('content', content($)),
       field('alternative', optional(alternativeBlock($))),
     )),