adds modifierMode parameter to typeof (#25815)

This PR adds 3 modes to `typeof` to specify how to handle type modifiers
`var`, `sink` and `lent`.

- typeOfModCompatible
Remove or keep type modifiers in the same way as old typeof. That means
keep `sink` but remove `var` and `lent`.
- typeOfModRemoveModifier
  Remove type modifiers.
- typeOfModKeepModifier
  Keep type modifiers.

Related to https://github.com/nim-lang/Nim/pull/25779
https://github.com/nim-lang/Nim/issues/25786

(cherry picked from commit 48621c217f)

lib/system.nim

@@ -54,7 +54,12 @@ type
     typeOfProc,      ## Prefer the interpretation that means `x` is a proc call.
     typeOfIter       ## Prefer the interpretation that means `x` is an iterator call.
 
-proc typeof*(x: untyped; mode = typeOfIter): typedesc {.
+  TypeOfModifiers* = enum  ## Modes to handle type modifiers `var`, `sink` and `lent`.
+    CompatibleTypeModifiers,  ## Remove or keep type modifiers in the same way as old typeof. That means keep `sink` but remove `var` and `lent`.
+    RemoveTypeModifiers,      ## Remove type modifiers.
+    KeepTypeModifiers,        ## Keep type modifiers.
+
+proc typeof*(x: untyped; mode = typeOfIter; modifierMode = CompatibleTypeModifiers): typedesc {.
   magic: "TypeOf", noSideEffect, compileTime.} =
   ## Builtin `typeof` operation for accessing the type of an expression.
   ## Since version 0.20.0.
@@ -76,6 +81,11 @@ proc typeof*(x: untyped; mode = typeOfIter): typedesc {.
       # since `typeOfProc` expects a typed expression and `myFoo2()` can
       # only be used in a `for` context.
 
+    proc varParam(x: var int;
+                  y: typeof(x, modifierMode = RemoveTypeModifiers);
+                  z: typeof(x, modifierMode = KeepTypeModifiers)) = discard
+    doAssert varParam is proc (x: var int; y: int; z: var int) {.nimcall.}
+
 proc `or`*(a, b: typedesc): typedesc {.magic: "TypeTrait", noSideEffect.}
   ## Constructs an `or` meta class.