Complete constructor keyword after property declaration (#43654)

* Complete `constructor` keyword after property declaration.

* Fix logical errors.

* Fix for more universal situations.

* Only provide completions if property declaration is terminated.

* Simplify many logical conditions.

* Make the fix more reliable.

* Narrowing the fix.

tests/cases/fourslash/completionConstructorKeywordAfterPropertyDeclaration.ts

@@ -0,0 +1,98 @@
+/// <reference path="fourslash.ts" />
+
+//// // situations that `constructor` is partly present
+//// class A {
+////   blah; con/*1*/
+//// }
+//// class B {
+////   blah
+////   con/*2*/
+//// }
+//// class C {
+////   blah: number
+////   con/*3*/
+//// }
+//// class D {
+////   blah = 123
+////   con/*4*/
+//// }
+//// class E {
+////   blah = [123]
+////   con/*5*/
+//// }
+//// class F {
+////   blah = {key: 123}
+////   con/*6*/
+//// }
+//// // situations that `constructor` is fully present
+//// class G {
+////   blah; constructor/*7*/
+//// }
+//// class H {
+////   blah
+////   constructor/*8*/
+//// }
+//// class I {
+////   blah: number
+////   constructor/*9*/
+//// }
+//// class J {
+////   blah = 123
+////   constructor/*10*/
+//// }
+//// class K {
+////   blah = [123]
+////   constructor/*11*/
+//// }
+//// class L {
+////   blah = {key: 123}
+////   constructor/*12*/
+//// }
+//// // situations that `constructor` isn't present, but we should offer it
+//// class M {
+////   blah; /*13*/ 
+//// }
+//// class N {
+////   blah
+////   /*14*/
+//// }
+//// // situations that `constructor` should not be suggested
+//// class O {
+////   blah /*15*/ 
+//// }
+//// class P {
+////   blah con/*16*/
+//// }
+//// class Q {
+////   blah: number con/*17*/
+//// }
+//// class R {
+////   blah = 123 con/*18*/
+//// }
+//// class S {
+////   blah = {key: 123} con/*19*/
+//// }
+//// type SomeType = number
+//// class T {
+////   blah: SomeType con/*20*/
+//// }
+//// const SomeValue = 123
+//// class U {
+////   blah = SomeValue con/*21*/
+//// }
+
+function generateRange(l: number, r: number) {
+  return Array.from(Array(r - l + 1), (_, i) => String(i + l)); // [l, r]
+}
+
+verify.completions({
+  marker: generateRange(1, 14),
+  includes: { name: "constructor", sortText: completion.SortText.GlobalsOrKeywords },
+  isNewIdentifierLocation: true,
+});
+
+verify.completions({
+  marker: generateRange(15, 21),
+  exact: [],
+  isNewIdentifierLocation: true,
+});