Migrate all use of gojsonschema to openapi

[Porges]

Describe the current behavior
See: #1548 (comment)

[matthchr]

This is still something we're thinking of doing (related to #2084)

[matthchr]

After the Swagger branch merges, we will need to fix our Golden file tests. (or we can fix it in the Swagger branch if we want that to be bigger)

[matthchr]

Swagger has merged but we still need to fix the golden tests

[matthchr]

We still want to do this. This is just for the tests really.

What we're currently thinking is, we do away with the generic JSON -> golden file tests, and instead swap these tests to use the new, more focused, RunTestPipeline based tests that @theunrepentantgeek started writing a while back.

[matthchr]

We should maybe consider breaking this out into individual test folders and assigning them owners over the next few releases to migrate.

[matthchr]

The work involved to make this fully go away to replace golden file tests with focused golden tests.

The test folders in question are:

• AdditionalProperties
• AllOf (@theunrepentantgeek) ?
• ArmResource (@matthchr)
• EmbeddedTypes (@matthchr)
• Enum
• EnumNames
• Flattening
• RecursiveTypes
• RemoveTypeAliasesPipeline
• UnreferencedDefinitions
• Validations