fix: support multiple minisearch widget instances

[DanielRuf]

Description

When cloning the minisearch widget and changing the ID's and selectors they still trigger all instances as the label searchLabel is globally searched instead of in the form.

Manual testing scenarios

1. clone module-search/view/frontend/templates/form.mini.phtml
2. add custom block with the cloned and changed minisearch widget (after changing ID's and selectors in it)
3. click on search icon on mobile

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[dmanners]

Hi @DanielRuf thank you for this PR. I have restarted the travis build to see if I can find the issue with it. After that I will process your PR.

[DanielRuf]

It seems Travis tries to clone from origin.

$ git clone --depth=5 --branch=fix/minisearch-widget-multiple-instances https://github.com/magento/magento2.git magento/magento2
Cloning into 'magento/magento2'...
warning: Could not find remote branch fix/minisearch-widget-multiple-instances to clone.
fatal: Remote branch fix/minisearch-widget-multiple-instances not found in upstream origin

[DanielRuf]

The issue was that Travis seems to reuse the commit hash and I've cherry-picked the commit (accidentally pushed it magento/magento2) so I've created a new PR (to clean it a bit up) and changed the commit hash with a new empty commit and git rebase.

[DanielRuf]

See #15485

[dmanners]

Interesting thanks for looking at it @DanielRuf