Add Class metadata models

[notaphplover]

Added

• Added ClassMetadata models.
• Added getClassMetadata.

Motivation

In order to migrate inversify, several responsibilities are being moved from inversify to @inversifyjs/core. The first one is metadata management.

Currently, inversify has this responsibility distributed among several modules, making hard figuring out what's expected to be stored as metadata:

• It's currently challenging to know what's the expected metadata associated to a type. inversify metadata internal data structures don't represent some edge cases (like the handling of lazy service identifiers).

• Several checks as enforcing no duplicated tags can be simplified with the right data structures.

• Code can be decoupled from reflect-metadata, making it more maintainable.

• This decoupling would unlock the implementation of better metadata representations. This can result in reducing the operations and the amount of objects involved in the process of planning the instantiation of a service, something that would result in the simplification of the source code and boosting the performance of the library.

• ClassMetadata is proposed as a data structure that represents the metadata associated to a certain type. This data structure handles in an efficient way most of the operations involved in the planning process.

Testability

Once this approach is discussed and validated, several tests must be included:

1. Unit tests should validate all the code flows with a decent mutation testing score.
2. E2E tests should enforce getClassMetadata is consistent with inversify's MetadataReader and Target.

[notaphplover]

Hey @rsaz , I've been analyzing the way inversify handles metadata in order to delegate that responsibility in this package. I've drafted this proposal, what do you think about it?