fix(snackbar): Doesn't close while other element is focused

[trimox]

Snackbar doesn't close when any element on page receives focus event while snackbar is opened and snackbar has empty action text.

reference: material-components/material-components-web#2183

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@9fba0ff). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #1242   +/-   ##
=========================================
  Coverage          ?   93.25%           
=========================================
  Files             ?      173           
  Lines             ?     6628           
  Branches          ?      970           
=========================================
  Hits              ?     6181           
  Misses            ?      447           
  Partials          ?        0

Impacted Files	Coverage Δ
packages/snackbar/snackbar.component.ts	90.17% <100%> (ø)

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