compiler: optimize constant expressions

[tpdenk]

Optimize constant expressions, so that the executor does not have to evaluate expressions like these.

• 1 == 2 => false
• false == true => false
• a IS b where a and b are different constant values => false
• 1 BETWEEN 5 AND 6 => false
• etc.

There is a lot of room for creativity here.
Please take note, that optimizations require extensive testing, so that nothing is optimized in a wrong way.
This means, that to complete this ticket, a lot of positive and negative test cases are required.