action/command: Prevent overwriting settings set locally or by plugin

- on `reload`
- on `filetype` change

internal/buffer/buffer.go

@@ -86,6 +86,8 @@ type SharedBuffer struct {
 
 	// Settings customized by the user
 	Settings map[string]interface{}
+	// LocalSettings customized by the user for this buffer only
+	LocalSettings map[string]bool
 
 	Suggestions   []string
 	Completions   []string
@@ -326,6 +328,7 @@ func NewBuffer(r io.Reader, size int64, path string, startcursor Loc, btype BufT
 		// assigning the filetype.
 		settings := config.DefaultCommonSettings()
 		b.Settings = config.DefaultCommonSettings()
+		b.LocalSettings = make(map[string]bool)
 		for k, v := range config.GlobalSettings {
 			if _, ok := config.DefaultGlobalOnlySettings[k]; !ok {
 				// make sure setting is not global-only