Merge asset-swapper with erc20-bridge-sampler

[dorothy-zbornak]

Description

Most of the file changes are just renames and deletions.

This moves the erc20-bridge-sampler contracts into packages/asset-swapper. The contracts/erc20-bridge-sampler package is no more. This should mean 0x-API no longer has to gitpkg contract-artifacts and contract-wrappers.

Also removed the sampler contract's dependency on DevUtils by inlining the fillable taker amount check on native orders.

Testing instructions

Types of changes

Checklist:

• [ ] Prefix PR title with [WIP] if necessary.
• [ ] Add tests to cover changes as needed.
• [ ] Update documentation as needed.
• [ ] Add new entries to the relevant CHANGELOG.jsons.

[coveralls]

Coverage decreased (-0.05%) to 79.523% when pulling f9c35f9c4271dc803da3968a68f76b7945dec6fe on feat/asset-swapper/merge-with-sampler into de675c173e906bc5137937252091eb2866762f1d on feat/mStable.