feat: Optionally hide deprecation errors

[dobromir-hristov]

Allows users to hide the deprecation warnings and hides them while our internal tests are run.

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.
• 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-test-utils/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:

[fredicious]

Allows users to hide the deprecation warnings

What would be the way to do that ? the config showDeprecationWarnings doesn't seem to be supported yet

[lmiller1990]

@fredicious it should work - did you do this:

import { config } from '@vue/test-utils'
config.showDeprecationWarnings = false

In your test setup file? It should disable for all the tests.

[fredicious]

that worked, thanks a lot @lmiller1990
Somehow I got confused between the main config and the mounting options.

[sullivanpt]

Not sure why, but this new import here breaks the IIFE. Would love some help tracking this down and fixing it. See #1553