Make all properties non-enumerable in spies, stubs, mocks and fakes

[ehmicky]

Purpose (TL;DR) - mandatory

Fix issue #1936 by making all properties non-enumerable in spies, stubs, mocks and fakes.

How to verify - mandatory

1. Check out this branch
2. npm install
3. sinon.spy(), sinon.stub(), sinon.fake(), sinon.mock() should not return non-enumerable properties.

Very few properties had to be left because removing them was breaking the tests.

Also this is a breaking change (major version) because some users might rely on spy/stub/fake/mock properties being enumerable.

CircleCI on Node 10 fails but this does not seem related to this PR, as it failed on other commits/PRs.

Checklist for author

• npm run lint passes
• References to standard library functions are cached.

[coveralls]

Pull Request Test Coverage Report for Build 2789

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 15 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.4%) to 94.118%

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Files with Coverage Reduction	New Missed Lines	%
sinon/mock.js	1	96.62%
sinon/spy.js	2	89.59%
sinon/stub.js	3	91.02%
sinon/util/core/wrap-method.js	9	79.41%

Totals
Change from base Build 2788:	-0.4%
Covered Lines:	1635
Relevant Lines:	1703

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💛 - Coveralls

[fatso83]

Very nice! This looks fine to me, as the diff is very understandable. Haven't tested it, though.

Not sure this change validates a test or not, as this should be a non-functional change.

[mroderick]

Thank you ❤️