vim: Allow trailing whitespace for :norm command (#46403)

Fix a bug with `:norm` that disallowed trailing whitespace.

Commands that accept generic args (defined with `args()`) now preserve
trailing whitespace, while commands that accept filenames (defined with
`filename()`) have whitespace pre-trimmed. This allows, for example, 
`:norm I  ` to correctly insert spaces, matching NeoVim's behavior.

Release Notes:

- vim: Fixed `:norm` command to preserve trailing whitespace in
arguments (e.g., `:norm I ` now correctly inserts two spaces)

---------

Co-authored-by: dino <dinojoaocosta@gmail.com>

crates/vim/test_data/test_normal_command.json

@@ -76,3 +76,17 @@
 {"Key":"enter"}
 {"Key":"u"}
 {"Get":{"state":"ˇThe quick\nbrown fox\njumps over\nthe lazy dog\n","mode":"Normal"}}
+{"Put":{"state":"ˇquick\nbrown fox\njumps over\nthe lazy dog\n"}}
+{"Key":":"}
+{"Key":"n"}
+{"Key":"o"}
+{"Key":"r"}
+{"Key":"m"}
+{"Key":"space"}
+{"Key":"I"}
+{"Key":"T"}
+{"Key":"h"}
+{"Key":"e"}
+{"Key":"space"}
+{"Key":"enter"}
+{"Get":{"state":"Theˇ quick\nbrown fox\njumps over\nthe lazy dog\n","mode":"Normal"}}