RFR: 8230623: Extract command-line help for -Xlint sub-options to new --help-lint [v2]

[Jonathan Gibbons]

I like the fact that you suggest the use of `--help-list`.

-- Jon

On 4/28/21 7:11 AM, Guoxiong Li wrote:
>    -Xlint:<key>(,<key>)*
>          Warnings to enable or disable, separated by comma.
>          Precede a key by - to disable the specified warning.
>          Use option --help-lint to see the supported keys.