gdb: rename 'enum range_type' to 'enum range_flag'

gdb: rename 'enum range_type' to 'enum range_flag'

To avoid confusion with other parts of GDB relating to types and
ranges, rename this enum to make it clearer that it is a set of
individual flags rather than an enumeration of different types of
range.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* expprint.c (print_subexp_standard): Change enum range_type to
	range_flag and rename variables to match.
	(dump_subexp_body_standard): Likewise.
	* expression.h (enum range_type): Rename to...
	(enum range_flag): ...this.
	(range_types): Rename to...
	(range_flags): ...this.
	* f-lang.c (value_f90_subarray): Change enum range_type to
	range_flag and rename variables to match.
	* parse.c (operator_length_standard): Likewise.
	* rust-exp.y (rust_parser::convert_ast_to_expression): Change enum
	range_type to range_flag.
	* rust-lang.c (rust_evaluate_funcall): Likewise.
	(rust_range): Likewise.
	(rust_compute_range): Likewise.
	(rust_subscript): Likewise.