app,io/router: expand IME snippets if a new range overlaps the old

Instead of cmpletely replacing the IME snippet for every update, expand
the old range if there is overlap. This change avoids never-ending
restarts of the IME on Android where snippets are expanded in two
calls, one for expanding before the selection and one for exanding after
the selection.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/window.go

@@ -492,7 +492,6 @@ func (c *callbacks) EditorInsert(text string) {
 func (c *callbacks) EditorReplace(r key.Range, text string) {
 	c.w.imeState.Replace(r, text)
 	c.Event(key.EditEvent{Range: r, Text: text})
-	c.Event(key.SnippetEvent(c.w.imeState.Snippet.Range))
 }
 
 func (c *callbacks) SetEditorSelection(r key.Range) {