edit predictions: Rename edit prediction modes (#25657)

`auto` -> `stealth`
`eager_preview` -> `eager`

Release Notes:

- N/A

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/language/src/language_settings.rs

@@ -244,10 +244,11 @@ pub struct EditPredictionSettings {
 pub enum EditPredictionsMode {
     /// If provider supports it, display inline when holding modifier key (e.g., alt).
     /// Otherwise, eager preview is used.
-    Auto,
+    Subtle,
     /// Display inline when there are no language server completions available.
     #[default]
-    EagerPreview,
+    #[serde(alias = "eager_preview")]
+    Eager,
 }
 
 #[derive(Clone, Debug, Default)]