VP-3148: Fix issues after migration to Open API v3 and latest Swashbuckle

[asvishnyakov]

Problems

We have a few problems because of migration to Open API v3 and latest Swashbuckle:

1. POST methods body isn't named and has unknown position in generated code (backward incompatibility with Storefront v4 API clients)
2. POST methods body isn't named when scheme generated with Open API v2 specification (backward incompatibility with Storefront v4 API clients)
3. All reference and nullable types isn't marked as nullable in schema
4. POST methods body is required. ASP.NET Core will return 415 error code if you will send request with empty body to API with [FromBody] attribute
5. Some parameters can be nullable, but is required.
6. Storefront dosn't add Newtonsoft.Json support to Swashbuckle and instead used some custom filters

Out of scope of this PR:
2. Because of bug in OpenAPI.NET library which Swashbuckle use for API schema generation and conversion from v2 to v3. The workaround for some tools is to use same vendor extensions (x- schema properties) as we use for v3 (see later). Extensibility of request body parameter in v2 also isn't supported currently, I made PR to OpenAPI.NET to support it.
5. I don't think it's something important just because it will make these parameters as union with undefined (string | undefined, for example). It allow do more, than possible, not less. So I created VP-3175 about that.

Solution

1. Use vendor extensions to add naming and position to request body in schema:
   1.1. x-name and x-position for NSwag
   1.2 x-codegen-request-body-name for Swagger Codegen. Position isn't support and not neccessary here because Swagger Codegen always put body to the end of generated methods, even for Open API v2.
   1.3. x-ms-requestBody-name and x-ms-requestBody-index for AutoRest.
2. Out of scope
3. Mark all reference and nullable types as nullable in schema
4. Mark all requestBody occurrences in schema as required
5. Out of scope
6. Properly configure Swashbuckle

Proposed changes

1. I added NameAndOrderRequestBody parameter to appSettings.json in Swagger:Schema section. If it's enabled, ParameterOrderFilter and NameAndOrderRequestBodyFilter filers for Swashbuckle will add vendor extensions to support body naming and positionning.
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-3b8759d90ee0adf1adf31373f4c91f68R357-R358
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-94cddb6036b2fc6ff8d4aebebe23c31e
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-63affde52279701e934521b33cb972ef
2. The only improvement is OpenApiSpecificationVersion parameter in Swagger:Schema section of appSettings.json which allow you to select which schema version should be produced. Unfortunately, we can't add new API version with new Open API specification version support - all versions will be generated with the same Open API specification.
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-2f1bd9bddcbb37bce32c91dcbd59948e
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-bbef13df0bbb66cd265aff04d91e7476R9
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-3b8759d90ee0adf1adf31373f4c91f68R429-R434
3. Swashbuckle has a bug about that. Workaround is to enable UseAllOfToExtendReferenceSchemas schema option which will make desired behavior.
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-3b8759d90ee0adf1adf31373f4c91f68R367
4. RequireRequestBodyFilter added to make all requestBody occurrences in schema as required
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-3b8759d90ee0adf1adf31373f4c91f68R359
   https://github.com/VirtoCommerce/vc-storefront-core/pull/441/files#diff-602d549f760206cd3d0f0882fcfe48ec
5. No changes
6. AddSwaggerGenNewtonsoftSupport method called during services configuration due to Swashbuckle readme. It also replace our OptionalParametersFilter and NewtonsoftJsonIgnoreFilter and produce more correct schema - for, example it exclude from schema proeprties marked with [IgnoreDataMember] like Customer, Currency or Language of CartSearchCriteria

Additional context (optional)

1. NSwag has bug, which prevent parameters ordering working right now, but I made PR to fix it.
2. NSwag uses NJsonScheme, which has a bug about incorrect processing null values, but I made PR to fix that
3. Swashbuckle use Microsoft OpenAPI.NET tool to generate API for v2, I created bug about support of this parameter and made PR to support extensions for body parameter - it's same workaround as for Open API v3.

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[Flanker72]

We don't need this anymore in newer vc-storefront releases.