refactor!: remove the default value for step

[vursen]

Description

This PR removes the default value for the step property of number-field which makes it possible to throw away the custom validation logic entirely relying on the InputConstraintsMixin validation logic instead.

Breaking changes:

1. The step property no longer has a default value and therefore undefined and null values are now allowed.
2. Setting the step property no longer leads to setting the step attribute on the number-field host.

Related to #1224

Type of change

• Refactor

Checklist

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

[web-padawan]

Let's remember to update corresponding ITs in the Flow components:

• IntegerFieldPageIT
• NumberFieldPageIT

Also, the logic that uses 1 as a fallback step value needs to be replicated in the Flow component, see for example how it's implemented in the TimePicker.

[sonarcloud]

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0 Bugs
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1 Code Smell

No Coverage information
0.0% Duplication

[vursen]

Let's remember to update corresponding ITs in the Flow components:

I checked on the Flow counterpart and looks like its step already defaults to 1 according to:

https://github.com/vaadin/flow-components/blob/d16cc31709b64be4dfc7e765c7e802b121c34253/vaadin-text-field-flow-parent/vaadin-text-field-flow/src/main/java/com/vaadin/flow/component/textfield/AbstractNumberField.java#L109

...so only tests will need to be updated. I'll take care of them during the next release.