[scanner] Ask VM to inline Token._setCommentParent

From the scanner benchmark with --bytes:

```
    N           Min           Max        Median           Avg        Stddev
x  25     135.49248     140.11327     137.90404     137.70731     1.1732525
+  25     135.55161     143.54553     141.81997     141.37336     1.8048844
Difference at 95.0% confidence
        3.66606 +/- 0.865817
        2.66221% +/- 0.628737%
        (Student's t, pooled s = 1.52219)
```

Change-Id: Ia69010d6215f59242b7f4e91d1af295cf4db1775
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/407421
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Jens Johansen <[email protected]>

Author: jensjoha

pkg/_fe_analyzer_shared/lib/src/scanner/token.dart

@@ -696,6 +696,7 @@ class SimpleToken implements Token {
    * Sets the `parent` property to `this` for the given [comment] and all the
    * next tokens.
    */
+  @pragma("vm:prefer-inline")
   void _setCommentParent(CommentToken? comment) {
     while (comment != null) {
       comment.parent = this;