feat: add conditional (non-attribute) selectors to ElementQueries

[joelpop]

Description

In contrast to ComponentQuerys of unit testing TestBench, ElementQuerys in E2E testing TestBench have (up until now) only provided attribute-based selector methods. This was expanded upon in PR #1774 to provide selector methods for common attributes, such as those for class names, theme, and id. This PR adds condition-based selector methods to ElementQuery to mirror and expand upon those of ComponentQuery. Namely:

• withCondition
• withPropertyValue[Containing]
• withLabel[Containing]
• withPlaceholder[Containing]
• withCaption[Containing]
• withText[Containing]

Elements having their labels in their text (such as buttons) must implement a new, method-less interface HasLabelAsText in their element tester (such as NativeButtonElement for the NativeButton component and ButtonElement for the Button component) in order for the withCaption[Containing] selectors to work for them.

This PR brings the E2E testing selectors up to par with the unit testing selectors. The only one missing is withValue.

Fixes #1183 Add Additional Selectors

Type of change

• [ ] Bugfix
• [x] Feature

Checklist

• [x] I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• [x] I have added a description following the guideline.
• [x] The issue is created in the corresponding repository and I have referenced it.
• [x] I have added tests to ensure my change is effective and works as intended.
• [x] New and existing tests are passing locally with my change.
• [x] I have performed self-review and corrected misspellings.

Additional for Feature type of change

• [x] Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.