Improve PSI initialization, add writing setup

[alexander-yevsyukov]

This PR improves the initialization of IntelliJ PSI environment allowing write operations.

• Environment object was introduced, using the setup code previously adopted for parsing in ProtoData.
• FileSystem object was introduced for creating PsiJavaFile from existing File.
• PsiWrite object was introduced as a façade for performing additional configuration of PSI required for handling operations that modify the PSI tree.