vim: Fix space not handling non-ascii characters (#27053)

Closes #26806

Changes: Clips the new point with `Bias::Right` like in
`saturating_right`

Release Notes:

- vim: Fixed `space` not handling non-ascii characters

crates/vim/test_data/test_space_non_ascii.json

@@ -0,0 +1,4 @@
+{"Put":{"state":"ˇπππππ"}}
+{"Key":"3"}
+{"Key":"space"}
+{"Get":{"state":"πππˇππ","mode":"Normal"}}