feat(snackbar): Add dismiss button

[emri99]

• Add property dismissible (default false) to avoid BC
• Update related test
• Update related screenshot

Related issue: #933

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[emri99]

@googlebot I signed it!

[codecov-io]

Codecov Report

Merging #999 into master will increase coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #999      +/-   ##
==========================================
+ Coverage   94.13%   94.14%   +<.01%     
==========================================
  Files          86       86              
  Lines        3649     3654       +5     
  Branches      578      581       +3     
==========================================
+ Hits         3435     3440       +5     
  Misses         90       90              
  Partials      124      124

Impacted Files	Coverage Δ
packages/snackbar/index.tsx	97.29% <100%> (+0.19%)	:arrow_up:

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