Add validation loosening awareness to all checks

[everettraven]

Some schema property checks only take into consideration validation tightening as a breaking change, but this isn't always the case.

Depending on how the API is used, there may be cases where you want to be:

• Strict on tightening of validations but not loosening
• Strict on loosening of validations but not tightening
• Strict on both loosening and tightening of validations