Implement Future aggregation functions.

[player-03]

These are based on JavaScript's promise concurrency functions, using Lime's nomenclature.

Supersedes #1844

[player-03]

@EliteMasterEric How do these look to you?

[player-03]

I'm going back and forth between calling it "allResolved" or "allSettled".

• Lime's Promise class consistently uses the term "resolve".
• We're copying JavaScript's functions, so it'd be more intuitive to use JavaScript's names.
• The function works slightly differently than the JS version, so maybe a slightly different name will make the change more obvious.
• Wikipedia uses the term "resolve".