Add scrollbar scroll-to-bottom test and fix existing scrollbar rendeing test

Author: tompng

test/reline/yamatanooroti/test_rendering.rb

@@ -1081,6 +1081,32 @@ def test_autocomplete_long_with_scrollbar_scroll
       EOC
     end
 
+    def test_autocomplete_super_long_scroll_to_bottom
+      start_terminal(20, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --autocomplete-super-long}, startup_message: 'Multiline REPL.')
+      shift_tab = [27, 91, 90]
+      write('S' + shift_tab.map(&:chr).join)
+      close
+      assert_screen(<<~'EOC')
+        Multiline REPL.
+        prompt> Str_BXX
+                Str_BXJ
+                Str_BXK
+                Str_BXL
+                Str_BXM
+                Str_BXN
+                Str_BXO
+                Str_BXP
+                Str_BXQ
+                Str_BXR
+                Str_BXS
+                Str_BXT
+                Str_BXU
+                Str_BXV
+                Str_BXW
+                Str_BXX▄
+      EOC
+    end
+
     def test_autocomplete_super_long_and_backspace
       start_terminal(20, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --autocomplete-super-long}, startup_message: 'Multiline REPL.')
       shift_tab = [27, 91, 90]
@@ -1090,15 +1116,15 @@ def test_autocomplete_super_long_and_backspace
       assert_screen(<<~'EOC')
         Multiline REPL.
         prompt> Str_BX
-                Str_BX
-                Str_BXA
-                Str_BXB
-                Str_BXC
-                Str_BXD
-                Str_BXE
-                Str_BXF
-                Str_BXG
-                Str_BXH
+                Str_BX █
+                Str_BXA█
+                Str_BXB█
+                Str_BXC█
+                Str_BXD█
+                Str_BXE█
+                Str_BXF█
+                Str_BXG█
+                Str_BXH█
                 Str_BXI
                 Str_BXJ
                 Str_BXK
@@ -1142,7 +1168,7 @@ def test_dialog_narrower_than_screen_with_scrollbar
         Multiline R
         EPL.
         prompt> Sym
-        String
+        String    █
         Struct    █
         Symbol    █
         StopIterat█