Improve wp_trim_excerpt by separate trim text feature and excerpt specificity

[momo360modena]

Create a new function wp_trim_text() and use it for wp_trim_excerpt().

This modification is really minor.

I see not why she could not be integrated into the version 3.0

We are in feature freeze for 3.0, nor is this a minor modification.

We'd be introducing a new function that a major filter would use. It would not only need to be thoroughly reviewed, but also analyzed for whether it makes sense for the most number of users and developers as written.

It's true...

But the final behavior is the same, thus the side effects are more than limited.

Closing as a duplicate of #16372. The patch on that ticket seems more reasonable.