Generates excerpt using core get_the_excerpt

[draganescu]

Description

Closes #19418

How has this been tested?

Tested locally in browser by making some posts with embedded tweets and then another using the latest posts block.

The way to test:

• make a post or more with some tweet embeds and some text.
• mare sure the embed is close to the start of the post.
• make a post and use the latest posts block
• set the block to show excerpt
• there should be no tweet links in the excerpt

Types of changes

The latest posts block does, I believe, two wrong things about the excerpt:

• in the server side renderer it uses a custom way to get the excerpt which bypasses the core function that among other things renders only allowed blocks, strips shortcodes and a lot more.
• in the client side renderer it gets the rendered excerpt and then wrongfully checks for the raw excerpt, which may be empty if post has no manual excerpt, resetting the rendered excerpt with the raw post content.

This is what this PR fixes.

[talldan]

@draganescu Would you be able to provide some testing instructions, what should I look out for when testing?

I might be doing something wrong, but I still see the tweet URL in the latest posts block:

[draganescu]

hey @talldan thanks for trying this out:

The way to test:

• make a post or more with some tweet embeds and some text.
• mare sure the embed is close to the start of the post.
• make a post and use the latest posts block
• set the block to show excerpt
• there should be no tweet links in the excerpt

Do not use the full content option, that is a different issue I think.

[draganescu]

So @talldan the problem you encountered is that in the Latest Posts block there was a fallback which used the full post in case there was an empty excerpt. Now, I am not sure this fallback is the best option.

If I select excerpt, and the excerpt:

• either shows the excerpt
• or makes one from the post itself

... then there is no reason for the fallback.

The filtering of blocks from content does not apply (and shouldn't) for full post content.

Can you retest? Should be OK now.

[ajitbohra]

Works as expected, code-wise LGTM 👍