feat(jest-helpers): add jest-helpers package

[QuiiBz]

Summary

Reviewers:

1. @matthprost

2. @DorianMaliszewski

Ping:

(If you want to ping somebody involved in this MR without requesting reviews)

1. @philibea

Summarize the feature concisely:

What is expected?

Add a new jest-helpers package to generate few helper methods instead of duplicating them in different projects.

Does this introduce a consequent breaking change?

No

[codecov]

Codecov Report

Merging #432 (750de15) into master (b59a375) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #432   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        15    +4     
  Lines          448       473   +25     
  Branches        71        75    +4     
=========================================
+ Hits           448       473   +25     

Impacted Files	Coverage Δ
...kages/jest-helpers/src/helpers/renderWithTheme.tsx	100.00% <100.00%> (ø)
...-helpers/src/helpers/shouldMatchEmotionSnapshot.ts	100.00% <100.00%> (ø)
...rc/helpers/shouldMatchEmotionSnapshotWithPortal.ts	100.00% <100.00%> (ø)
packages/jest-helpers/src/index.ts	100.00% <100.00%> (ø)

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