Tweak the way the terminal widget ends scrolling

Thanks to @Peter2121 for this implementation!

Prior to this change, if the user hit the terminal hot-key and scrolled
back up then back down to the prompt again, a further keypress - q or Q
- would still be required to end scroll-mode. This brings the terminal
widget more in-line with other terminal implementations in that
scroll-mode is now ended automatically if the user scrolls back to the
prompt; no extra keypress needed by default.

I have added a new option to the terminal Options struct to preserve the
legacy behavior, if you need it - KeyPressToEndScrollMode (default
false).

widgets/terminal/terminal.go

@@ -129,14 +129,16 @@ type title struct{}
 type hotkey struct{}
 
 type Options struct {
-	Command              []string
-	Env                  []string
-	HotKey               IHotKeyProvider
-	HotKeyPersistence    IHotKeyPersistence // the period of time a hotKey sticks after the first post-hotKey keypress
-	Scrollback           int
-	Scrollbar            bool            // disabled regardless of setting if there is no scrollback
-	HotKeyFns            []HotKeyInputFn // allow custom behavior after pressing the hotkey
-	EnableBracketedPaste bool
+	Command                 []string
+	Env                     []string
+	HotKey                  IHotKeyProvider
+	HotKeyPersistence       IHotKeyPersistence // the period of time a hotKey sticks after the first post-hotKey keypress
+	Scrollback              int
+	Scrollbar               bool            // disabled regardless of setting if there is no scrollback
+	HotKeyFns               []HotKeyInputFn // allow custom behavior after pressing the hotkey
+	EnableBracketedPaste    bool
+	KeyPressToEndScrollMode bool // set to true to enable legacy behavior - when the user has scrolled
+	// back to the prompt, still require a keypress (q or Q) to end scroll-mode.
 }
 
 // Widget is a widget that hosts a terminal-based application. The user provides the
@@ -379,9 +381,18 @@ func (w *Widget) Scroll(dir ScrollDir, page bool, lines int) {
 	} else {
 		lines = w.canvas.ScrollBuffer(dir, false, gwutil.SomeInt(lines))
 	}
-	// Scrolling is now true if it (a) was previously, or (b) wasn't, but we
-	// scrolled more than one line
-	w.isScrolling = w.isScrolling || lines != 0
+
+	wasScrolling := w.isScrolling
+	if lines != 0 {
+		w.isScrolling = true
+	} else if !w.params.KeyPressToEndScrollMode && dir == ScrollDown {
+		// Disable scroll if we are at the bottom and we tried to scroll down
+		// Thanks @Peter2121 !
+		w.isScrolling = false
+	}
+	if wasScrolling && !w.isScrolling {
+		w.ResetScroll()
+	}
 }
 
 func (w *Widget) ResetScroll() {