fix(mdUtil): move comment nodes as well when disabling scroll

[gustavohenke]

As comment nodes were not moved by disableScrollAround(), Angular could
misplace a few elements because of a forgotten comment node that points
to a directive.

Fixes #2456

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[gustavohenke]

Signed.

[googlebot]

CLAs look good, thanks!

[gustavohenke]

Sorry, I incorrectly changed the file via GitHub, this patch will not work.
I'll fix and squash locally in a minute.

[gustavohenke]

Now it'll be okay.

[rschmukler]

Thanks @gustavohenke