fix: always use microtasks for nextTick

[haoqunjiang]

fix #7109, #7546, #7707, #7834, #8109
reopen #6566

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[haoqunjiang]

Note:
This PR also reopens #6690, which has a workaround #6740

[nicolaskopp]

Very late to the game, but this change did indeed introduce a breaking change, because it interferes with Cleave.js and updated input events (e.g. nextTick firing before InputField changes were properly populated). (Also see nosir/cleave.js#459 )

Solution: https://javascript.info/event-loop#macrotasks-and-microtasks

Before this change, something like this worked:

onValueChanged({ target }) {
      this.$nextTick(() => {
         // stuff
      });
}

Now you need to invoke a MacroTask:

onValueChanged({ target }) {
      setTimeout(() => {
         // stuff
      });
 }