fix(ivy): ng-container with ViewContainerRef creates two comments

[devversion]

With Ivy, injecting a ViewContainerRef for a <ng-container> element
results in two comments generated in the DOM. One comment as host
element for the ElementContainer and one for the generated LContainer
which is needed for the created ViewContainerRef.

This is problematic as developers expect the same anchor element for
the LContainer and the ElementContainer in order to be able to move
the host element of <ng-container> without leaving the actual
LContainer anchor element at the original location.

This worked differently in View Engine and various applications might
depend on the behavior where the ViewContainerRef shares the anchor
comment node with the host comment node of the <ng-container>. For
example CdkTable from @angular/cdk moves around the host element of
a <ng-container> and also expects embedded views to be inserted next
to the moved <ng-container> host element.

See: https://github.com/angular/components/blob/f8be5329f8d94128ece5dfe3e8e998fe4077d44d/src/cdk/table/table.ts#L999-L1016

Resolves FW-1341

[pkozlowski-opensource]

@devversion thnx, the change itself LGTM. I was just wondering if you could add an acceptance test for the exact use-case that was discovered in Material (moving around comment node). WDYT?

[devversion]

@pkozlowski-opensource Thanks for reviewing. The acceptance test I added should already cover that scenario. It's not an exact test-case but covers the exact same use-case. can you please re-check and let me know if this is sufficient? Thanks!

[kara]

LGTM, one optional nit

[kara]

presubmit

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[kara]

merge assistance: code fresh delayed

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