Refactor the code so that fzf can be used as a library (#3769)

src/tui/dummy.go

@@ -8,7 +8,7 @@ func HasFullscreenRenderer() bool {
 	return false
 }
 
-var DefaultBorderShape BorderShape = BorderRounded
+var DefaultBorderShape = BorderRounded
 
 func (a Attr) Merge(b Attr) Attr {
 	return a | b
@@ -29,7 +29,7 @@ const (
 	StrikeThrough = Attr(1 << 7)
 )
 
-func (r *FullscreenRenderer) Init()                              {}
+func (r *FullscreenRenderer) Init() error                        { return nil }
 func (r *FullscreenRenderer) Resize(maxHeightFunc func(int) int) {}
 func (r *FullscreenRenderer) Pause(bool)                         {}
 func (r *FullscreenRenderer) Resume(bool, bool)                  {}