* In `@0x/contracts-exchange`: Add `SignatureType.OrderValidator` support to contracts and refactor signature validation functions.
* In `@0x/types`: Add `SignatureType.OrderValidator` and `RevertReason.InappropriateSignature`.
* In `@0x/contracts-exchange`: Fix contracts and update tests for `SignatureType.OrderValidator`.
* Ran prettier/linter
* Update changelogs
* In `@0x/order-utils`: Add `SignatureOrderValidatorError` to `ExchangeRevertErrors`.
* In `@0x/contracts-exchange`: Add `SignatureOrderValidatorError` rich revert. Fix rebase issues. Rename `IValidator.isValidOrder` to `IValidator.isValidOrderSignature`.
* In `@0x/contracts-exchange`: Add revert test cases for `OrderValidator` signature type.
* In `@0x/order-utils`: Update changelog.
* In `@0x/contracts-exchange`: Split off `SignatureType.OrderValidator` scheme into its own interface and registry.
* In `@0x/types`: Add `SignatureType.WalletOrderValidator`.
* In `@0x/order-utils`: Add `SignatureWalletOrderValidatorError`.
* In `@0x/contracts-exchange`: Add `SignatureType.WalletOrderValidator` support.
* Ran prettier
* In `@0x/types`: Remove `RevertReason.WalletOrderValidator`.
* Update/fix changelogs in `@0x/contracts-exchange`, `@0x/order-utils`, and `@0x/types`.
* In `@0x/contracts-exchange`: Make `isValidOrderSignature` `external` instead of `public`.
* In `@0x/contracts-exchange`: Change `isValidOrderSignature` back to `public` because passing `calldata` to internal functions isn't supported.