Support multiple adaptors in the compiler

[josephjclark]

Short Description

This PR enables the compiler to generate import statements for two adaptors.

This basically just means turning the adaptor option (which days which adaptor to use) into adaptors and making it an array. This turns out to have a huge ripple effect in the typings but it's sorted now: the "entry points" tend to ensure that adaptors is an array, massing the original input in to the right format.

One issue which arises out of this work is the possibility of conflict. If you import http and fhir, for example, do we import fn from http or fhir? Fortunately with collections we don't really need to address this issue. But if somehow it ever does come up, it'll result in compiled javascript code being invalid. So we can deal with this later.

This is part of #777

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[josephjclark]

Ah ok - we need to add support for multiple adaptors in the engine as part of this PR, because the engine's call into the compiler is now wrong

[josephjclark]

The size of the diff here is really escalating! The work is fairly trivial but far reaching and requires close thought. Hopefully get it wrapped on Monday

[josephjclark]

Phew! I think this is done. Changed my strategy on how to do this several times 😊