This patch vendors the sources from Go 1.17.13's encoding/json
package in the package vim25/json.

This patch introduces support for discriminators to the "encoding/json" package.
A discriminator is a field in a JSON object that indicates the object's type.
For example:

        {
            "breed": "Lab"
        }

The above JSON does not indicate the Go type into which the object should be
decoded. However, it is possible to store that Go type information along with
the JSON:

        {
            "_typeName": "Dog",
            "breed": "Lab"
        }

The "_typeName" field teaches the JSON decoder to unmarshal the object into the
Go type named "Dog".

This patch introduces functions for the json.Encoder and json.Decoder that may
be used to active support for discriminators.

This patch adds Go's LICENSE file to the vendored JSON package.

This patch adds a README to the vendored JSON package describing
its purpose and how to show the diff between the original sources
and the patch applied to the vendored copy.

This patch excludes the vendored vim25/json package from the
GitHub action that checks code style for Go sources.

This patch updates the type generation code to support adding
JSON tags to generated type field data.

BREAKING:

Updating the `vim25/types` with camelCased, JSON tags affects
the output of the `govc` command when using the `-json` flag
to emit results as JSON. Field names that used to be PascalCased
will now be camelCased. Queries for tools that parse JSON, such
as `jq`, will need to be updated to use the new camelCased fields.

This patch adds support to GoVmomi for marshaling/unmarshaling
the vim25/types (and other VMODL1 types) to/from JSON using:

* a customized version of the Golang encoding/json package that
  relies upon...
* a new discriminator field added to every every complex object
  marshaled to JSON, the "_typeName" field. this field's value
  must match the value of the type's registered type name from
  the type registry