bugfix(textarea): keep the same border width at rest, hover and focus

[Cuervino]

Fixes CUI-50.

In Firefox a TextArea is 2px wider and 2px taller at rest than on hover or focus, so the box shrinks and everything laid out below it jumps up by 2px as soon as the pointer arrives. Chromium is not affected.

The component only declared border-color at rest, so the width and the style came from the browser default: 2px inset on Firefox, 1px solid on Chromium. Both :hover and :focus set a full 1px border, hence the jump. Declaring the shorthand at rest makes the three states the same size everywhere, and replaces Firefox's inset relief with the flat border the theme intends.

Measured in Firefox, 1440px window:

State	Before	After
rest	620 x 76, 2px inset	618 x 74, 1px solid
hover	618 x 74	618 x 74
focus	618 x 74	618 x 74

InputV2 and InlineInput already declare an explicit 1px solid border at rest, so this aligns TextArea with the rest of the library.

[bert-e]

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[bert-e]

Waiting for approval

The following approvals are needed before I can proceed with the merge:

• the author

• one peer

Peer approvals must include at least 1 approval from the following list:

• @PierreAlexandreDelgado

• @sanassicisse

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[Cuervino]

/approve

[bert-e]

I have successfully merged the changeset of this pull request
into targetted development branches:

• ✔️ development/1.0

Please check the status of the associated issue CUI-50.

Goodbye cuervino.

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