Enable CI builds

[idg10]

• add submodule for JSON Schema test suite
• modified default test settings to use schema files from submodule
• added pipelines and scripted build
• removed local settings files from repo
• disabled automatic building of benchmark code on each test execution

[idg10]

Currently we have these packages:

Name	Usage
Corvus.Json.ExtendedTypes	.NET types representing typed JSON values with specializations such as JsonDateTime and JsonUuid
Corvus.Json.JsonSchema	Generated object model for JSON Schema (currently 2019-09 and 2020-12 drafts)
Corvus.Json.JsonSchema.TypeBuilder	Generates .NET source code from JSON Schemas
Corvus.Json.JsonSchema.TypeGeneratorTool	Command line tool wrapper around Corvus.Json.JsonSchema.TypeBuilder
Corvus.Json.Walker	Walks JSON documents, with support for references
Corvus.JsonHelpers	Utilities for working with JSON

I'm not sure Corvus.JsonHelpers should really exist. Only Corvus.Json.ExtendedTypes uses it. That library exposes EncodedContentMediaTypeParseStatus through one public member, and consumes JsonConstants and JsonReaderHelper as an implementation detail. It feels like putting this into a published library puts us on the hook for ongoing support for what should really be internal implementation details.

Note: we had a bit of a mixture of names starting Corvus.Json, Corvus.Json.SchemaSomething, and Corvus.JsonSchema.Something. For the packaged projects, I've gone with a consistent Corvus.Json prefix on everything (except Corvus.JsonHelpers which I'm not sure should exist) and a Corvus.Json.JsonSchema prefix for things concerned specifically with JSON Schema.

[idg10]

OK, that last commit takes us down to this:

Name	Usage
Corvus.Json.ExtendedTypes	.NET types representing typed JSON values with specializations such as JsonDateTime and JsonUuid
Corvus.Json.JsonSchema	Generated object model for JSON Schema (currently 2019-09 and 2020-12 drafts)
Corvus.Json.JsonSchema.TypeBuilder	Generates .NET source code from JSON Schemas
Corvus.Json.JsonSchema.TypeGeneratorTool	Command line tool wrapper around Corvus.Json.JsonSchema.TypeBuilder
Corvus.Json.Walker	Walks JSON documents, with support for references