This commit adds new helper functions under `Utils::CmdLineParser` to
parse a given ASCII string as different simple types, namely signed or
unsigned integers of different bit lengths (`uint8/16/32/64`, and
`int8/16/32`). The new functions validate that the parsed value fits
within the supported range of the expected int type. This commit also
adds different flavors of `ParseAsHexString()` to parse a hex string
into sequence of bytes (with fixed/known size or unknown size allowing
or disallowing truncation). It also moves the parse related methods
(like `ParseAsIp6Prefix`) from CLI modules in `CmdLineParser`.
The CLI modules are then updated to use the new `ParseAs{Type}`
functions simplifying the code and adding extra checks when parsing
the CLI input.
Finally, this commit adds a unit test `test_cmd_line_parser` verifying
the behavior of new `ParseAs{Type}()` functions.
Jonathan Hui