TYPO3 Core

This story is a parent issue of further FormEngine development. Bug fixes after main patch are handled with #69617

Main FormEngine:

• Everything around FormDataCompiler is for fetching, creating, adding and manipulating data. A huge array is returned.

• The data array is then given to "render part", the container / element structure.

Main goals:

• The data provider in FormDataCompiler should work on as little "external" data as possible, use and enrich the given data array with small provider classes that focus on single pieces of the result array.

• Data provider should be unit tested as much as possible. Basically every change in this area should be reflected by test changes, too.

• In the end, the "render part" should not do any $GLOBALS access anymore or fetch additional data via db requests or similar. It should only work on the given data array to render result data.

Secondary goals:

• Streamline the HTML output.

• Simplify array structures.

• Reduce dependencies to third party code, especially to BackendUtility.