Fix excluded file creation (#12620)

Fixes https://github.com/zed-industries/zed/issues/10890

* removes `unwrap()` that caused panics for text elements with no text,
remaining after edit state is cleared but project entries are not
updated, having the fake, "new entry"
* improves discoverability of the FS errors during file/directory
creation: now those are shown as workspace notifications
* stops printing anyhow backtraces in workspace notifications, printing
the more readable chain of contexts instead
* better indicates when new entries are created as excluded ones


Release Notes:

- Improve excluded entry creation workflow in the project panel
([10890](https://github.com/zed-industries/zed/issues/10890))

crates/collab/Cargo.toml

@@ -107,4 +107,5 @@ theme.workspace = true
 unindent.workspace = true
 util.workspace = true
 workspace = { workspace = true, features = ["test-support"] }
+worktree = { workspace = true, features = ["test-support"] }
 headless.workspace = true