xgettext: Java: Improve the support of the method .formatted().

xgettext: Java: Improve the support of the method .formatted().

* gettext-tools/src/x-java.c (enum token_type_ty): New enum items
token_type_conditional, token_type_colon, token_type_assign,
token_type_operator.
(phase5_get): Recognize all kinds of operators that may occur in expressions.
(extract_parenthesized): Invoke new_sub_region instead of inheriting_region.
Handle 'return' keyword specially. Invoke set_format_flag_on_region instead of
iterating through the region. When encountering an operator, close the
inner_region and open a new inner_region.
* gettext-tools/tests/xgettext-java-8: Add many more test cases.