Support String Templates

Formatting a source file with [String Templates](https://openjdk.org/jeps/459):

````java
class Foo {

    private static final int X = 42;
    private static final String Y = STR."\{X} = \{X}";

}
````

gives:
> Foo.java:4:45: error: did not generate token "."
