Allow AST matches in clang-query to have a trailing comma at the end of
matcher arguments. Makes it nicer to work with queries that span
multiple lines.
So, for example, the following is possible:
```clang-query
match namedDecl(
isExpansionInMainFile(),
anyOf(
varDecl().bind("var"),
functionDecl().bind("func"),
# enumDecl().bind("enum"),
),
)
```
