fix(cdk/drag-drop): throw if drop list or handle are set on a non-element node

[crisbeto]

Currently if a cdkDropList or cdkDragHandle is attached to a non-element node, a cryptic error is thrown. These changes add a proper error, similar to the one we have on cdkDrag.

Fixes #13540.

[jelbourn]

LGTM

[Achilles1515]

@crisbeto
What is the following check doing?
(typeof ngDevMode === 'undefined' || ngDevMode)

If I understand ngDevMode correctly,

typeof ngDevMode === 'undefined' will be true when in production mode.
ngDevMode will be true (NgDevModePerfCounters object) when in development mode.

So this is specifically checking for if ngDevMode has been manually set to false?

[crisbeto]

The typeof check is necessary, because ngDevMode might not be defined in ViewEngine apps. JS in strict mode throws an error when trying to access an undefined global variable.

[Achilles1515]

So (typeof ngDevMode === 'undefined' || ngDevMode) is expected to return:

VE (maybe just some...?)
true

IVY
prod - true
dev - true

What is the purpose?

[crisbeto]

It'll always be true for VE and in Ivy it'll get replaced to (typeof null === 'undefined' || null) which Terser is smart enough to remove, because it's considered dead code.

[Achilles1515]

Ah, okay. So ngDevMode is like a #define C macro during compilation.
Great timing on this article, too.

Thanks for the response.

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