Debugging match with 'when' causes false stepping point

[dsyme]

Debugging this code:

type U = 
   | A1 of int
   | A2 of int
   | A3 of int
   | A4 of int

let testFunc f u = 
    match u with 
    | A1 n -> f n
    | A2 n when n > 4 -> f n // this is hit
    | A2 n -> f n
    | A3 n -> f n
    | A4 n -> f n

testFunc id (A3 4)

fsc.exe -g --optimize- --terms --tailcalls- a.fsx 
devenv /debugexe a.exe

and stepping steps through the line "// this is hit" before continuing. THis is a false step - the code f n on that line is never hit.

The cause is that when we split pattern matching into chunks (e.g. A2, A3, A4) here https://github.com/dotnet/fsharp/blob/main/src/fsharp/PatternMatchCompilation.fs#L1419 the "continue" expression doesn't have a debug range. That means its initial code gets the debug range of the "A2 when" clause.

[dsyme]

Fixed in #11981