#316 Introduce small common position class in scanning and parsing

Second attempt at introducing the small common position class. Changes wrt to the previous attempt.

• No messy commit history.
• Common position class is now common.java.TextPosition.
• Dropped the smart common.java.strings.SORTER equality notion in TextPosition, setext.runtime.SyntaxWarning and common.typechecker.SemanticProblem as case-insensitivity smartness was not properly reflected in the hashCode` override.
• Cleaned out several PositionUtils functions as they completely moved to TextPosition.
• Adressed all points made in the review of !271 (closed)

Closes #316 (closed) !271 (closed)