Misleading warning for ?? throw.

[lrhn]

The code x ?? throw 0 gives the following errors:

ERROR|SYNTACTIC_ERROR|...file.dart|3|8|Expected to find ';'
ERROR|SYNTACTIC_ERROR|...file.dart|3|8|Expected an identifier

This is misleading since the real solution to the errors is to add parentheses around the throw 0 expression.
Listing what you expect to find is great, but it should be complete then, and '(' is also possible here.

[askeksa-google]

Will become a duplicate of #24891 when the analyzer integrates with the CFE.

[srawlins]

And so it is done. Duplicate of #24891.