Fix possessive "its" in docs and comments (#3998)

This PR fixes a number of places where we were incorrectly using "it's"
where we needed to use the possessive "its".

Release Notes:

- N/A

crates/editor/src/editor.rs

@@ -7050,7 +7050,7 @@ impl Editor {
         let buffer = self.buffer.read(cx).snapshot(cx);
         let selection = self.selections.newest::<usize>(cx);
 
-        // If there is an active Diagnostic Popover. Jump to it's diagnostic instead.
+        // If there is an active Diagnostic Popover jump to its diagnostic instead.
         if direction == Direction::Next {
             if let Some(popover) = self.hover_state.diagnostic_popover.as_ref() {
                 let (group_id, jump_to) = popover.activation_info();