debug_step instruction in latest SIL version

[Abdulraheem-Arar]

The debug_step instruction was added to the newer swift version and not in the older swift 5.8 SIL version. So a new case class should be handled in the SILparser for swan.

This is how the SIL snippet is in the SIL/instructions.md for swift 5.8.

sil-instruction ::= debug_step

debug_step

The case class for this should be added under the debug information under the debug_value case class.