refactor: rename implicitly typed variable types appropriately
new helper methode for MatrixSyntaxElement
abstract from implicit var declarations

When checking if a variable is assigned before use, certain
exceptions of variables that are implicitly initialized have
to be taken into account. Instead of handling each such case
separately, add a new interface for this purpose.
implement ImplicitVariableInitializer in for-loop, subset and typeset expressions
fix e9f75067: missing method renamings
fix typo