compat downgrade fixes

Downgrade fixes (compat rules)

Status: planned for 1.38.1.

The reverse of the modernize fixes. Each compat rule reports a construct the run's target compiler cannot compile, and its fix rewrites it to classic syntax: X := if C then A else B back to an if statement, X is not T to not (X is T), A not in S to not (A in S), S.Contains(Sub) to Pos(Sub, S) > 0, InRange(X, A, B) to (X >= A) and (X <= B), digit separators removed, and inline var declarations hoisted into the routine's var section.

A compat rule runs exactly when the target is older than its construct (compat_since), so one switch -- --target-compiler -- both silences the modernize advice and enables its reverse; the pair is never active together. The fixes run like every other fix: lint <file> --fix --target-compiler 12 is a dry run, --apply writes.

The 1.38.0 engine already has the switch, the compat category and the compat_since sidecar key; the rules ship in 1.38.1.