Improve the style variation control aria-label

[afercia]

Fixes #11044.

The accessible name of an UI control should match (or at least start with) the visible label. For more details please refer to the related issue #11044.

• changes the aria-label from Apply style variation "%s" to %s style
• this way, the visible label is at the beginning of the accessible name
• simplifies the wording, "apply" and "variation" are a bit redundant: we're already in a group identified as "Block Styles" so simplifying to, for example "Regular style" and "Large style", reduces noise for screen reader users
• adds a missing translators comment

From a l10n perspective, the variable at the beginning may not be ideal but it's essential for a11y reasons. I also wonder if we should add some info in the translators comment to inform translators to not move the variable and keep it at the beginning. /Cc @SergeyBiryukov @ocean90

[ocean90]

If it's that essential we should probably only use the actual label of the style for aria-label without any suffix.

[afercia]

@ocean90 thanks, makes sense. The panel title "Block Styles" will be always announced so repeating "style" is a bit pointless.