Create subpaths for "next" & "deprecated" components

[jpuzz0]

Describe the feature
As a part of an effort to update or deprecate components, new directories within react-core's src can be made and subpaths can be utilized so that users of new (yet to be formally released in a major version) and deprecated (yet to be completely phased out until the next major release) can access each respectively from the following:

• @patternfly/react-core/next
• @patternfly/react-core/deprecated

Any other information?
No components would be shipped as a part of this change, it would just be the scaffolding/configuration changes. When updates are made in patternfly-org to accommodate for "next" module components, we'll be able to demonstrate "React next" examples alongside existing component examples with the same names.