Component test fixes

These are all the test fixes that I made when I tried (unsuccessfully) to rebase #730 and add tests on it. After this MR, #1051 (closed) will be the only, and the largest, issue with component tests.

• Add all the missing RouterLinkStubs that were causing warnings, close #1050 (closed)
• Switch from the deprecated this.$nextTick() to calling the global nextTick helper
• Use findAllComponents, getComponent and findComponent to get specific classes from vue-test-utils that allow us to test a stubbed component's props, which unskips some tests
• Fix some TypeErrors that were showing up in the test logs but were not thrown, because Vue loves to be as unfriendly as possible in unit tests
• Unskip some tests by using Chai's isDefined and isUndefined helpers to look for the disabled attribute, since the handling of this attribute changed in Vue 3
• Unskip some more tests that now work just fine 🤷

This un-skips 23 tests, leaving 43 still skipped.