## `smithy.openapi#specificationExtension`
Adds a meta trait `smithy.openapi#specificationExtension` that can be used to annotate traits to indicate they should be serialized into specification extension (`x-*`) properties when converting to OpenAPI. This is supported on shapes, operations, and services. By default the extension will be named by the shape ID replacing `#` & `.` with `-` prefixed with `x-`, otherwise the extension can be specified using the `as` property.
A new package `smithy-openapi-traits` is introduced to contain the `smithy.openapi#specificationExtension` trait.
## `JsonSchemaMapper` and `JsonSchemaShapeVisitor`
BREAKING CHANGE: Technically, `JsonSchemaMapper` has a breaking change from a functional interface to a normal interface, but we are anticipating customers are not using `JsonSchemaMapper` as a functional interface since it was not annotated with `@FunctionalInterface`.
`JsonSchemaMapper` is updated to use `updateSchema(JsonSchemaMapperContext, Schema.Builder)` in `JsonSchemaShapeVisitor`, which will call the existing `updateSchema(Shape, Schema.Builder, JsonSchemaConfig)` by default when not implemented for backwards compatibility.
## `smithy-openapi`
Support is added for `smithy.openapi#specificationExtension` by implementing `SpecificationExtensionsMapper` for operations and services and updating `OpenApiJsonSchemaMapper` for shapes.
---------
Co-authored-by: Steven Yuan <yuasteve@amazon.com>
0ce4187cb1