feat(locales): add mergeLocales utility

[ST-DDT]

Part 1 of

• Remove locale switching support #1340
• Introduce a way to get details about missing locale data when using them #893

This PR provides a method that merges multiple locales into a single one.

Future PRs will:

• remove the fallback logic from the Faker class (Remove locale switching support #1340)
• change the way the locale is set in the Faker instances (Remove locale switching support #1340)
• actually throw for missing locale entries (Introduce a way to get details about missing locale data when using them #893)

[codecov]

Codecov Report

Merging #1707 (1dd8e63) into next (47b2cfc) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #1707   +/-   ##
=======================================
  Coverage   99.63%   99.63%           
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  Files        2336     2337    +1     
  Lines      241141   241178   +37     
  Branches     1088     1098   +10     
=======================================
+ Hits       240257   240294   +37     
  Misses        863      863           
  Partials       21       21           

Impacted Files	Coverage Δ
src/utils/merge-locales.ts	100.00% <100.00%> (ø)