Fix: Symbol based properties in arrays causes toEqual to throw

[mweststrate]

Summary

toEqual matcher could not handle symbol based properties in array's, causing jest to throw:

Minimal example:

    const mySymbol = Symbol("test");
    const actual1 = [];
    actual1[mySymbol] = 3;
    const expected = [];
    expected[mySymbol] = 3;

    expect(actual1).toEqual(expected);

Throws:

 TypeError: allKeys[x].match is not a function

      at Object.test (packages/expect/src/__tests__/matchers.test.js:456:21)

The cause of this issue is this line which assumes that all property names of arrays are strings and hence .match can be called on them.

This assumption does not held for symbol based properties. If the property name is a symbol, it is never an index, so it should always be added to the extraKeys collection.

Test plan

I added a unit test demonstrating that deep equality on arrays behaves correctly now, even in the presence of symbolic properties.

[SimenB]

Just add a FlowFixMe comment above this, flow is wrong.

[mweststrate]

Pushed, used //$FlowFixMe. Hopefully that is correct, I am flow noob :)

[rickhanlonii]

Great find

[codecov-io]

Codecov Report

Merging #6391 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6391   +/-   ##
=======================================
  Coverage   63.48%   63.48%           
=======================================
  Files         227      227           
  Lines        8697     8697           
  Branches        4        3    -1     
=======================================
  Hits         5521     5521           
  Misses       3175     3175           
  Partials        1        1

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[mweststrate]

N.B.: #6392 is quite related, I am willing to PR that one as well, but wanted to verify that the solution direction is correct first

[mweststrate]

Solved merge conflicts in last commit, no further changes

[github-actions]

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