What problem does this address?

Table block originally implemented captions as figcaption elements, due to limitations with RichText output discussed here: #15554

These limitations no longer apply, so nothing prevents us from using an actual table caption element instead. This makes tables more accessible for screen readers, as the caption content will be announced at the start of the table.

What is your proposed solution?

Change the table block markup to use caption as first element within the table element, instead of the current figcaption.

Consider adding a default content to the caption, such as we have on Navigation block name: Table 1, Table 2, etc..