DCOM-308: Create a Mapping Component

[doctrinebot]

Jira issue originally created by user @Ocramius:

All of the ORM/ODM projects currently rely on bi-directional mapping of:

• one column (persistence layer) <-> one object property
• one column (persistence layer) <-> one embeddable property
• multiple columns (persistence layer) <-> one embeddable property
• multiple columns (persistence layer) <-> one object property
• one column (persistence layer) <-> multiple property
• one column (persistence layer) <-> multiple embeddable properties
• one column (persistence layer) <-> an association
• multiple columns (persistence layer) <-> an association
  ... and more

Hibernate ORM seems to abstract this logic with a Property and a Column abstractions, each being a visitable DSL ( accept($value, $orm) , or similar).

This sort of DSL would be:

• a good replacement for DBAL types
• a good embeddable hacks
• a good replacement for association hydration logic
• a good replacement for identifier mapping

We could need a mapping component that allows mapping any map-alike data-structure to any php object graph.

[doctrinebot]

• depends on DCOM-307: Create a "Code Inliner" component for inlining function calls
• is required for DDC-3983: Replace metadata factory with pre-runtime (constructor-injected) metadata map