Inferred missing properties use resolved generic types rather than staying generic

<!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.3.0-dev.20181212 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** declare property generic missing member **Code** ```ts class TestClass<T> { // Inferred: // otherValue: number; public constructor( public readonly value: T, ) { } } const foo = new TestClass<number>(1); foo.otherValue = foo.value; ``` **Expected behavior:** `Declare property 'otherValue'` should create `otherValue: T;` **Actual behavior:** ...but it actually creates `otherValue: number`. Whatever generic type from the place you request the missing property be added will be the type of the property. **Playground Link:** http://www.typescriptlang.org/play/#src=class%20TestClass%3CT%3E%20%7B%0D%0A%20%20%20%20%2F%2F%20Inferred%3A%0D%0A%20%20%20%20%2F%2F%20otherValue%3A%20number%3B%0D%0A%20%20%20%20public%20constructor(%0D%0A%20%20%20%20%20%20%20%20public%20readonly%20value%3A%20T%2C%0D%0A%20%20%20%20)%20%7B%20%7D%0D%0A%7D%0D%0A%0D%0A%0D%0Aconst%20foo%20%3D%20new%20TestClass%3Cnumber%3E(1)%3B%0D%0A%0D%0Afoo.otherValue%20%3D%20foo.value%3B%0D%0A **Related Issues:** I found a _lot_ of similar bugs but didn't see any that looked related...