Specify input range by byte offsets

[soutaro]

Instead of adding a character offset calculation in (#2859), I'd like to propose specifying byte offset for the input range of the RBS parser.

Parser.parse_type(input, byte_range: 0...256)       # byte_range is byte offset
Parser.parse_type(input, range: 0...50)             # range is character offset, automatically translates to byte offset for compatibility in Ruby code

Closes: #2859

[ksss]

Is it related? #1814

[soutaro]

Maybe... but it was not in my mind.