Anticipate 2 block related filters deprecation in WP 5.8

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WordPress ​5.8 is scheduled to July 2021, it's one month later than the date we planned to release 8.0.0.

In WP 5.8, the block_categories & block_editor_settings are deprecated. I suggest to anticipate it using the attached patch.

[imath]

In 12944:

BP Blocks: anticipate 2 deprecated WP 5.8 Block filters

In WordPress 5.8, the block_categories filter is deprecated in favor of the block_categories_all one and the block_editor_settings filter is deprecated in favor of block_editor_settings_all. To maintain backward compatibility with previous versions of WordPress, we are now checking if two functions introduced in WP 5.8 (get_default_block_categories() & get_block_editor_settings()) exists before using the right filters.

Fixes #8465

[imath]

Ouch!

While running a last round of test after packaging the 8.0.0-beta2, I noticed the block_categories_all filter has not the same argument types than the deprecated one. There's some extra work to do there to make sure the BuddyPress block category will be registered in WP 5.8

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In 12956:

BP Blocks: make sure the BuddyPress category is available in WP >= 5.8

As blocks are always loaded even if the category is not available, there's no more interest in disabling the BuddyPress category. As a result we deprecated the bp_block_category_post_types filter.

Fixes #8465