Rationalize GitHub/CodeQL-proposed precision and security-severity properties

[michaelcfanning]

GitHub Advanced Security accepts property bag-delivered values in its system to specify results precision and security level.

It would be good to rationalize these property values with current SARIF and to incorporate them, if appropriate, into the 2.2 update.

@adityasharad @lcartey

https://docs.github.com/en/code-security/code-scanning/integrating-with-code-scanning/sarif-support-for-code-scanning#runautomationdetails-object
https://github.blog/changelog/2021-07-19-codeql-code-scanning-new-severity-levels-for-security-alerts/

[adityasharad]

@michaelcfanning I've created separate component issues for precision and security-severity.

[adityasharad]

Closing in favour of #611 and #612.