Add @sandbox to Metadata Comparison

[deevroman]

If I understood correctly, this is some analog of @inject-into, so I placed it right after it

https://www.tampermonkey.net/documentation.php#meta:sandbox

[erosman]

MAIN, ISOLATED, & USER_SCRIPT are MV3 contexts.
FireMonkey is still on MV2, since the MV3 userScripts API is still not fully ready.

Furthermore, userScripts.ExecutionWorld only has MAIN & USER_SCRIPT.

ISOLATED belongs to scripting.ExecutionWorld and not suitable for userscripts.

Finally, the decision on world injection in MV3 depends on the @grant and not selectable by userscript developers.
That would probably mean that both @inject-into & @sandbox may become obsolete in MV3.