Add a "label-suffix" slot

[heruan]

Implementation of #212.

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This change is 

[tomivirkki]

I would suggest you to write a custom extension for this feature instead. Including this feature in the core text-field element would require a lot of consideration regarding Lumo/Material themes and since it's a new feature and also could be considered a breaking change, this can't be included during the ongoing beta period.

[heruan]

Thank you @tomivirkki for the feedback. I understand that merging this in beta period might be unwise due to possible breaking changes, but do you feel this might have a chance to be considered after beta (thus left open)?

Having this as an extension will force to extend also any other elements using vaadin-text-field (such as vaadin-combo-box, vaadin-date-picker, vaadin-dropdown-menu), to enable this feature there.

[tomivirkki]

A breaking change would in practice require a new major release so unfortunately it's unlikely to make it in <vaadin-text-field> 2.X.

[heruan]

I tried to avoid breaking changes, in fact I don't understand entirely which part of the changes you consider would break existing code using the element. I'm wrapping the label part in a div, but part="label" is still targetable, so existing themes unaware of the wrapper shouldn't break.

[heruan]

@tomivirkki any feedback about what may break merging this PR? I'm willing to try to rework this, if the feature is something you'd consider at least.

[tomivirkki]

If you open the "Lumo Theme" demo page with the change in place, you can see that the labels are no longer properly aligned in the "Small Size" example:

There might be other such cases that could get easily unnoticed. Since it's in practice a new feature and quite a fundamental change to the internal structure, it would be too risky for us to merge it this close to releasing the stable version.

[heruan]

FWIW, I just fixed the label size issue for vaadin-text-area in the latest commit (not showing up here since the PR is closed now).