Refactor and simplify expressions plugin in NP

[streamich]

• Move most of the code into /common folder, so same implementation is shared by browser and server.
• Remove all imports from @kbn/interpreter.
  • Refactor Registry class
    • Use new Map to store items by ID.
    • Remove .wrapper()
    • Remove .getProp (if possible)
  • Inline what we need to keep from @kbn/interpreter.
    • fromExpression and toExpressions - still importing these but created wrappers and re-exporting those.
    • getType
    • getByAlias
    • castProvider
    • Ast
    • Registry
    • other
  • Remove .toJS() from registries
  • Remove unnecessary functions like initializeInterpreter() and interpretAst(), replace by run() function.
• Completely refactor interpreterProvider() function
  • Do not mutate AST in irreversible way.
• Rename expression function context to input.
• Rename handlers to context.
• Use state containers
  • State container to store expressions plugin state (registries)
  • New state container for each expression "execution"

Could have:

• Rename context field in function definition to inputTypes.
• Instantiate Expression service on server-side, just to see it is working.
• Add README.
• Simplify highest level interfaces (loader, renderer).

Follow up work:

• Move @kbn/interpreter PEG.js build step to expressions plugin.
• Move @kbn/interpreter toExpression() function to expressions plugin.
• Remove ExpressionDataHandler in favor of Execution.

Parent issue: #46909

[elasticmachine]

Pinging @elastic/kibana-app-arch