Fix a lot of incorrect behaviors

[joelwurtz]

Fixed

• Use the MapFrom attribute reference instead of MapTo when resolving transformers in MapFromListener
• Do not run a transformation on a null source value when the target is not nullable, a TypeError is thrown for typed properties instead of the transformation crashing on the null value
• Create backed enum from scalar source value instead of assigning the raw scalar
• Convert between different backed enums through their backing value instead of copying the source instance
• Normalize leading backslash in class names resolved from docblocks, fixing a parse error in generated mappers for global namespace classes and the __PM__ proxy name off-by-one
• Implement CheckTypeInterface on enum, date-time and uid transformers so union source types generate a runtime check for every branch
• Unwrap nullable doctrine collection target type, items are mapped to the collection value type instead of plain arrays
• Capture the context in the isAllowedAttribute closure, fixing MapToContext combined with skip_null_values
• Guard nested property accessors (parent.child) against null or uninitialized parent values on read, write and constructor paths, support private nested leaf properties and nullable parent types
• Support variadic constructor parameters, values are spread as individual arguments and an absent variadic no longer throws MissingConstructorArgumentsException
• The highest priority Mapper attribute wins as documented, instead of the lowest
• Correct identifier hashing: scalar identifiers are cast to string, object identifiers are hashed through their own mapper and hash_final no longer receives a string as its boolean argument, fixing mappers generated with strictTypes: true
• Atomic mapper file writes and locked registry updates in FileLoader, fixing partially written files and lost registry entries under concurrency, the cache warmer no longer discards previously registered mapper hashes
• Initialize LazyMap only once instead of re-running the mapping on every access
• Align Map attribute if condition semantics with symfony/object-mapper: if: false never maps the property, callables receive the value first and class level Map targets also match child classes
• Do not register the cache warmer when the eval loader is enabled, fixing container compilation with automapper.loader.eval: true
• Detect doctrine entities even when their metadata is not loaded yet, fixing missing provider and identifier on cold metadata factories
• Do not map static properties