[#4774] Normalize textfield component's value

[vaszig]

Closes #4774

Changes

• Added a regression test for the component's normalizer
• Implemented the normalizer method for the component

The prefill module was already normalizing the components' values but for the textfield component we were missing the normalizer method.

Checklist

Check off the items that are completed or not relevant.

• Impact on features

  • [x] Checked copying a form
  • [x] Checked import/export of a form
  • [x] Config checks in the configuration overview admin page
  • [x] Problem detection in the admin email digest is handled

• Release management

  • [x] I have labelled the PR as "needs-backport" accordingly

• I have updated the translations assets (you do NOT need to provide translations)

  • [x] Ran ./bin/makemessages_js.sh
  • [x] Ran ./bin/compilemessages_js.sh

• Commit hygiene

  • [x] Commit messages refer to the relevant Github issue
  • [x] Commit messages explain the "why" of change, not the how

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.56%. Comparing base (a755cd5) to head (b0917f3). Report is 15 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #4775 +/- ## ======================================= Coverage 96.56% 96.56% ======================================= Files 746 746 Lines 25210 25215 +5 Branches 3322 3324 +2 ======================================= + Hits 24345 24350 +5 Misses 602 602 Partials 263 263 ```

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[sergei-maertens]

Backports:

• 2.8.x: ad2a2f824b81b25e8daad6e9f7c694d994488eb3
• 2.7.x: e78c9df836209a646ee3590212ddd39306cb9c22