Add Has_Side_Effect function for place holders

[pjljvandelaar]

We need a function to determine whether a place holder (which points to an expression)
has a side effect.

We can start with a simple version that
states that a function call always has a side effect,
reading constants and variable has not side effect,
and operators have a side effect when one of there arguments has a side effect.

[pjljvandelaar]

Closed by
15bdc08

Note: some improvements are still possible

• Analyze whether function call indeed has side effect
  • (in-)out parameters
  • write to non-local variable
  • write to file / screen / ...
• Handling Attribute_Ref
  • see e.g. https://en.wikibooks.org/wiki/Ada_Programming/Attributes/%27Pos that an attribute is a function.
  • Can one implement it own 'Image function in Ada 2022?