Add reference to originating locations in YAML specs - step 1

[reuvenharrison]

This PR adds the ability to correlate OpenAPI components with the location in the originating YAML spec.
Here's a summary of the changes required to achieve this:

1. Modify yaml.v3 to add line and column numbers of each YAML element to the unmarshaled interfaces (see https://github.com/oasdiff/yaml3)
2. Modify invopop/yaml with a new function: UnmarshalWithOrigin (see https://github.com/oasdiff/yaml)
3. Modify this repo to add an Origin struct to OpenAPI components. This requires changes to the UnmarshalJSON functions and, in some cases, replacing native types, like map[string]string, by dedicated types that include the original native type and an Origin member.

This PR addresses issue #986

Follow up tasks to be addressed by future PRs:

• Add origin to more elements, namely Components and some types that are unmarshalled with unmarshalStringMapP or unmarshalStringMap
• Merge changes in yaml.v3 and invopop/yaml back to original repos and remove replace directives from go.mod
• Enhance origin to include end line and column and YAML comments as proposed by @fenollp