chore(deps): bump core-js from 3.9.1 to 3.12.1 in /showcase

[dependabot]

Bumps core-js from 3.9.1 to 3.12.1.

Changelog

Sourced from core-js's changelog.

3.12.1 - 2021.05.09

• Fixed some cases of Function#toString with multiple core-js instances
• Fixed some possible String#split polyfill problems in V8 5.1

3.12.0 - 2021.05.06

• Added well-known symbol Symbol.metadata for decorators stage 2 proposal
• Added well-known symbol Symbol.matcher for pattern matching stage 1 proposal
• Fixed regression of V8 ~ Node 0.12 String(Symbol()) bug, #933

3.11.3 - 2021.05.05

• Native promise-based APIs Promise#{ catch, finally } returns polyfilled Promise instances when it's required

3.11.2 - 2021.05.03

• Added a workaround of WebKit ~ iOS 10.3 Safari Promise bug, #932
• Promise#then of incorrect native Promise implementations with correct subclassing no longer wrapped
• Changed the order of Promise feature detection, removed unhandled rejection tracking check in non-browser non-node platforms

3.11.1 - 2021.04.28

• Made instanceof Promise and .constructor === Promise work with polyfilled Promise for all native promise-based APIs
• Added a workaround for some buggy V8 versions ~4.5 related to fixing of %TypedArray% static methods, #564

3.11.0 - 2021.04.22

• Added accessible Object#hasOwnProperty stage 2 proposal
  • Object.hasOwn method
• Fixed a possible RegExp constructor problem with multiple global core-js instances

3.10.2 - 2021.04.19

• URL and URLSearchParams marked as supported from Safari 14.0
• Polyfilled built-in constructors protected from calling on instances

3.10.1 - 2021.04.08

• Prevented possible RegExp#split problems in old engines, #751, #919
• Detection of Safari 10 string padding bug extended to some Safari-based browsers

3.10.0 - 2021.03.31

• Array find from last proposal moved to the stage 2, March TC39 meeting
• Prevented possible RegExp#exec problems in some old engines, #920
• Updated compat data mapping:
  • NodeJS up to 16.0
  • Electron up to 13.0
  • Samsung Internet up to 14.0
  • Opera Android up to 62
  • The rest automatically

Commits

• 8752e69 3.12.1
• 3eb4159 fix some possible String#split polyfill problems in V8 5.1
• 1789d3e fix some cases of Function#toString with multiple core-js instances
• c7170fb update eslint-plugin-regexp
• 1aadb7b 3.12.0
• 9f8ff89 fix regression of V8 ~ Node 0.12 Sting(Symbol()) bug, close #933
• b3afb28 add Symbol.matcher
• 98e421f add Symbol.metadata
• bfe345a 3.11.3
• f26cd0b native promise-based APIs Promise#{ catch, finally } returns polyfilled `Pr...
• Additional commits viewable in compare view

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[dependabot]

A newer version of core-js exists, but since this PR has been edited by someone other than Dependabot I haven't updated it. You'll get a PR for the updated version as normal once this PR is merged.

[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.