Allow filtering the alignment options of blocks via `theme.json`

[oandregal]

Related https://github.com/WordPress/gutenberg/issues/34316

The align options of blocks can be filtered using the block_type_metadata filter. It'd be easier for themes if they could filter those options via theme.json as we do with other settings such as units.

[oandregal]

Ran this by Riad and this is the context I've gathered:

• themes now define layout.contentWidth and layout.wideSize which already control the visibility of the alignment controls
• float options (left, center, right) are unaffected by the existing layout (they are always visible if the block supports it)
• disabling alignment options per block can be confusing to users
• we have different layout options (flow, flex) and alignments are contextual to the particular layout

I'm not sure we want to do this yet.

[fabiankaegy]

From my perspective, the ability to filter the alignment options of blocks via theme.json would be a significant improvement. It currently is the primary thing the blocks.registerBlockType hook in JS gets used for.

function addWideAlignmentOptions(settings, name) {
    if (name !== 'namespace/block-name') {
        return settings;
    }

    return {
        ...settings,
        attributes: {
            ...settings.attributes,
            align: {
                'wide',
                'full'
            },
        },
    };
}

addFilter(
    'blocks.registerBlockType',
    'add-wide-alignment-options',
    addWideAlignmentOptions,
);

Not having to manually filter the options but instead having a more declarative way of achieving this would reduce a lot of code that by nature is modifying settings at a relatively low level in the block API.