marking a field with noInit allows to skip constructor initialiser (#22802)

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

tests/cpp/tnoinitfield.nim

@@ -0,0 +1,30 @@
+discard """
+  targets: "cpp"
+  cmd: "nim cpp $file"
+  output: '''
+'''
+"""
+{.emit: """/*TYPESECTION*/
+  struct Foo {
+    Foo(int a){};
+  };
+  struct Boo {
+    Boo(int a){};
+  };
+
+  """.}
+
+type 
+  Foo {.importcpp.} = object
+  Boo {.importcpp, noInit.} = object
+  Test {.exportc.} = object
+    foo {.noInit.}: Foo
+    boo: Boo
+
+proc makeTest(): Test {.constructor: "Test() : foo(10), boo(1)".} = 
+  discard
+
+proc main() = 
+  var t = makeTest()
+
+main()