Implements: [C++] constructor pragma improvement (fix #21921) (#21916)

* implements: [C++] constructor pragma improvement (fix #21921)

t

* fix test so it doesnt use echo in globals

* Update compiler/ccgtypes.nim

* Update lib/std/private/dragonbox.nim

---------

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

tests/cpp/tconstructor.nim

@@ -1,6 +1,9 @@
 discard """
   targets: "cpp"
   cmd: "nim cpp $file"
+  output: '''
+1
+'''
 """
 
 {.emit:"""/*TYPESECTION*/
@@ -15,10 +18,38 @@ struct CppClass {
 };
 """.}
 
-type  CppClass* {.importcpp.} = object
+type  CppClass* {.importcpp, inheritable.} = object
   x: int32
   y: int32
 
 proc makeCppClass(x, y: int32): CppClass {.importcpp: "CppClass(@)", constructor.}
+#test globals are init with the constructor call
+var shouldCompile {.used.} = makeCppClass(1, 2)
 
-var shouldCompile = makeCppClass(1, 2)
+proc newCpp*[T](): ptr T {.importcpp:"new '*0()".}
+
+#creation
+type NimClassNoNarent* = object
+  x: int32
+
+proc makeNimClassNoParent(x:int32): NimClassNoNarent {. constructor.} =
+  this.x = x
+  discard
+
+let nimClassNoParent = makeNimClassNoParent(1)
+echo nimClassNoParent.x #acess to this just fine. Notice the field will appear last because we are dealing with constructor calls here
+
+var nimClassNoParentDef {.used.}: NimClassNoNarent  #test has a default constructor. 
+
+#inheritance 
+type NimClass* = object of CppClass
+
+proc makeNimClass(x:int32): NimClass {. constructor:"NimClass('1 #1) : CppClass(0, #1) ".} =
+  this.x = x
+
+#optinially define the default constructor so we get rid of the cpp warn and we can declare the obj (note: default constructor of 'tyObject_NimClass__apRyyO8cfRsZtsldq1rjKA' is implicitly deleted because base class 'CppClass' has no default constructor)
+proc makeCppClass(): NimClass {. constructor: "NimClass() : CppClass(0, 0) ".} = 
+  this.x = 1
+
+let nimClass = makeNimClass(1)
+var nimClassDef {.used.}: NimClass  #since we explictly defined the default constructor we can declare the obj