local implies yielding

[dkalinichenko-js]

Make yielding mode the default if local is set. The change is only limited to syntax parsing and does not change the inference code. To preserve consistency, the global modality/modifier now also implies unyielding by default, and [@local_opt] also varies along the yielding axis.

Subsequent PRs will add yielding annotations to the Capsule API and to the Effects API.

The printer now displays stack_ allocation return values with @ unyielding, as intended.

This change sometimes causes principal and non-principal type inference to diverge when the old syntax for local_ annotations is used. I'm surprised this compiler option affects syntax parsing, but the issue seems benign.

[dkalinichenko-js]

@riaqn I'd appreciate help debugging the divergence between principal and non-principal typing here, I can't figure out why it happens.

[riaqn]

The principality issue is because some types (for example, string) is immutable_data and crosses yielding. Let's discuss offline.

[dkalinichenko-js]

I changed legacy zapping behavior of yielding to vary based on areality too. This fixed the differences between principal and non-principal typing, so I'm happy to merge this now.

[dkalinichenko-js]

I also changed contents of lazys to always be unyielding in addition to global. Otherwise, existing code that relies on the contents of a local lazy_t being at the legacy mode would break.

[dkalinichenko-js]

Fixed the issue you pointed out + print order.

[riaqn]

Could you check again if any diff can be minimized? (since the commits has gone back and forth).
Then I think it's good to go.