[ LatestPosts ] Display full manual excerpts in the editor

[draganescu]

Is your feature request related to a problem? Please describe.
Manual excerpts should not be truncated, nether in the editor nor in the rendered content.

Describe the solution you'd like
#20313 implements a sample excerpt_length filter which allows the server side rendering of the LatestPosts block to respect how excerpts are currently handled by WordPress.

As discussed in the design channel on Slack we should stick to the following process:

• blocks that work with excerpts, right now PostExcerpt and LatestPosts
• should default to the global excerpt setting (set by the excerpt_length) filter
• but have a local setting
• which only affects their rendered content
• but only generated excerpts
• manual excerpts should be rendered integrally, independent of what the excerpt_length setting is.

This behavior is both consistent to how WordPress currently handles excerpts and also with what a user would expect from the system.