fix(drawer): missing elevation shadow

[crisbeto]

Fixes the elevation box shadow not being applied to drawers.

Fixes #8386.

[mmalerba]

fixes #6528

[jelbourn]

Caretaker note: potential screenshot diffs

[nueko]

Halo,
Iam using multiple themes and the elevation gone

<mat-toolbar color="primary" class="mat-elevation-z6"></mat-toolbar>

and fixed with adding z-index

<mat-toolbar color="primary" class="mat-elevation-z6" style="z-index: 6"></mat-toolbar>

is this pr fix that issue?

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