Add new LinearCodeAddressGenerator contract

[turbolent]

Port the linear code address generator from https://github.com/onflow/flow-go/blob/master/model/flow/address.go to Cadence.

We'll likely need this for the migration code of onflow/cadence#3584, which will be implemented as a Cadence contract.

[sisyphusSmiling]

Left a couple clarifying questions. My main question is whether index needs to be tracked in contract or some struct's state or if that's relegated to some lower-level state.

[sisyphusSmiling]

Approved but CI failing. Looks like the go assets need to be updated as well.

[tarakby]

I'm back from time off and looking at this today

[tarakby]

Nice!

[bluesign]

Nit: I think address(index: 0) should fail

[tarakby]

Nit: I think address(index: 0) should fail

right thanks @bluesign.
Actually, address(index) should only work for index in the range [1 .. 2^45 - 1], and should fail otherwise.

[turbolent]

@tarakby Added a check for the index in 7fb76ed

[tarakby]

Sweet! Thank you @turbolent, feel free to merge

[joshuahannan]

Can you add a bit more docs comments to this contract to make it more clear what the purpose of each part is? Thank you!

[turbolent]

The public functions have docstrings, and the private functions are implementation details. I only ported the Go code over, I'm not an expert in the details of how the underlying code works.

[joshuahannan]

okay. Can you add a little blurb about it in the README with intended import addresses also like there is for other contracts? Once that is added, I'm okay with you merging it