This change prototypes shifting from separately maintained schemas inthe `schemas` folder to deriving fully expressed schemas from the Ruststructs in the code.Doing so requires using the alpha release of schemars v1, which addedsupport for more easily defining schemas using attributes and supportsderiving schemas adhering to the JSON Schema 2020-12  specification.Of particular note are the following changes to the JSON Schema forinstances of the registry resource:- Use JSON Schema specification draft 2020-12 instead of draft 07.- Added `title` and `description` for every property as documentation.- Added a regular expression check for `keyPath` to ensure it starts  with a valid hive identifier.- Added the `$id` keyword to ensure that users and integrating  developers can get a copy of the schema online instead of always  calling the command.- Marked the `keyPath` property as required.- Marked the `valueName` property as required _only when_ `valueData`  is specified.- Marked the `_metadata` property and its `whatIf` sub-property as  read-only.- Defined the default value for the `_exist` property as `true`.In the process of implementing this prototype, this change alsoaddressed a few related challenges:- In order to define longer strings for documentation keywords in the  schemas, this change uses the `rust_i18n` library to provide a way  to map complex or lengthy strings to key names. This also prepares  the project for internationalization and localization, though the  change only defines translations for English.- To minimize rework, the struct attributes define the JSON Schema  with VS Code's annotation keywords, which enhance the authoring and  editing experience in VS Code, but are generally ignored by other  tools and libraries. To account for the difference between the  canonical (stictly 2020-12 compatible) schema and the enhanced schema  this change also:  1. Adds the `--enhanced` option to the `registry schema` command to     enable returning the enhanced schema, but default to returning     the canonical schema as is current behavior.  1. Defines the `remove_vscode_keywords` function to recursively     remove those keywords. While the function is implemented in the     registry resource in this prototyping PR, it better belongs in     `dsc_lib`.  1. Defines the `get_schema_generator` function to return a generator     with the correct settings for canonical and enhanced schemas. In     both cases, it no longer adds the `null` type for optional items     in the struct to better conform with JSON Schema. In JSON Schema,     specifying `null` for a property value is _not_ semantically the     same as _not_ specifying the property. For the enhanced schemas,     it also uses `definitions` instead of `$defs`, as VS Code doesn't     understand retrieving references from `$defs`.This change shows how we can begin to:1. Define full, enhanced JSON schemas for data types in Rust and export   those schemas in both canonical and enhanced variants.1. Migrate from in-code strings to referencing data keys, making it   easier to change documentation and messages without editing the code   and preparing the projects for internationalization and localization.1. Define reusable helpers for the projects to minimize rework.The scope of these changes is limited to the registry project only.

This change exports the registry schemas to the repository for onlinereview without requiring a user or integrating developer to installthe package and invoke the `registry schema` command.