[clang] [Clang][Sema] Reject undeduced static data members without initializers (#173349) (PR #174281)

[Hamza Hassanain via cfe-commits]

HamzaHassanain wrote:

@zwuis 

Switched from checking `Type->isUndeducedType()` to `Type->getContainedDeducedType()` 
. 

As far as I understand:

`isUndeducedType()` looks at `E`, sees it's an alias, and returns false because `E` itself isn't technically a "deduced type" node until you unwrap it.

So, should I leave it as `Type->isUndeducedType()`  and find another condition to force calling `Sema::DeduceVariableDeclarationType`  (so as to call `deduceVarTypeFromInitializer` to hit the place where we handle `E`, `U`)

https://github.com/llvm/llvm-project/pull/174281