Bump core-js from 3.9.0 to 3.15.1 in /backend

[dependabot]

Bumps core-js from 3.9.0 to 3.15.1.

Changelog

Sourced from core-js's changelog.

3.15.1 - 2021.06.23

• Fixed cloning of regex through RegExp constructor, #948

3.15.0 - 2021.06.21

• Added RegExp named capture groups polyfill, #521, #944
• Added RegExp dotAll flag polyfill, #792, #944
• Added missed polyfills of Annex B features (required mainly for some non-browser engines), #336, #945:
  • escape
  • unescape
  • String.prototype.substr
  • Date.prototype.getYear
  • Date.prototype.setYear
  • Date.prototype.toGMTString
• Fixed detection of forbidden host code points in URL polyfill
• Allowed rhino target in core-js-compat / core-js-builder, added compat data for rhino 1.7.13, #942, thanks @​gausie
• .at marked as supported from FF90

3.14.0 - 2021.06.05

• Added polyfill of stable sort in { Array, %TypedArray% }.prototype.sort, #769, #941
• Fixed Safari 14.0- %TypedArray%.prototype.sort validation of arguments bug
• .at marked as supported from V8 9.2

3.13.1 - 2021.05.29

• Overwrites get-own-property-symbols third-party Symbol polyfill if it's used since it causes a stack overflow, #774
• Added a workaround of possible browser crash on Object.prototype accessors methods in WebKit ~ Android 4.0, #232

3.13.0 - 2021.05.26

• Accessible Object#hasOwnProperty (Object.hasOwn) proposal moved to the stage 3, May 2021 TC39 meeting

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

... (truncated)

Commits

• d7409d1 3.15.1
• aa66fb2 fix cloning of regex through RegExp constructor, close #948
• 4f7f304 3.15.0
• 219b688 fix dotAll entry
• bae33e0 revert test of delegation to .exec().groups in .replace
• 9a91e18 some stylistic changes
• bccff54 some protections
• e485690 some improvements
• f7b619d simplify fix-regexp-well-known-symbol-logic
• 3646a74 some improvements
• Additional commits viewable in compare view

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[dependabot]

Superseded by #532.