Parse Kotlin Code with Class fields instead of maps

[Matthias]

Objective.

• Make it possible to parse existing Json files into Kotlin objects.
• Foundation for a Monstera transpiler to parse Json files into Kotlin/Monstera code
• Make build data more accessible to plugin developers

Required changes

• All base files need to open the unsafe context and mark fields with annotations to be included in the build files.
• a new build strategy for gson (no build maps, annotations for key-value pairs)

Breaking changes

• The unsafe context is deprecated.
• Move unsafe.build() to the root of the file.
• Backward compatibility for MonsteraFile can't be supported.