Utilities: Add half-page scrolling + number modifiers to 'less'

- 'u' and 'd' now scroll up and down half a page
- Typing a number followed by 'j', 'k', 'return', 'up' or 'down' will
  scroll that many lines in the appropriate direction
- Typing a number followed by 'g' or 'G' will scroll directly to the
  line corresponding to that number

Userland/Utilities/less.cpp

@@ -158,9 +158,30 @@ public:
 
     void bottom()
     {
+        while (read_line())
+            ;
         down_n(m_lines.size() - m_line);
     }
 
+    void up_half_page()
+    {
+        up_n(m_height / 2);
+    }
+
+    void down_half_page()
+    {
+        down_n(m_height / 2);
+    }
+
+    void go_to_line(size_t line_num)
+    {
+        if (line_num < m_line) {
+            up_n(m_line - line_num);
+        } else {
+            down_n(line_num - m_line);
+        }
+    }
+
     void init()
     {
         while (m_lines.size() < m_height) {
@@ -371,22 +392,46 @@ int main(int argc, char** argv)
 
     pager.init();
 
+    StringBuilder modifier_buffer = StringBuilder(10);
     for (String sequence;; sequence = get_key_sequence()) {
-        if (sequence == "" || sequence == "q") {
+        if (sequence.to_uint().has_value()) {
-            break;
+            modifier_buffer.append(sequence);
-        } else if (sequence == "j" || sequence == "\e[B" || sequence == "\n") {
+        } else {
-            pager.down();
+            if (sequence == "" || sequence == "q") {
-        } else if (sequence == "k" || sequence == "\e[A") {
+                break;
-            if (!emulate_more)
+            } else if (sequence == "j" || sequence == "\e[B" || sequence == "\n") {
-                pager.up();
+                if (!modifier_buffer.is_empty())
-        } else if (sequence == "g") {
+                    pager.down_n(modifier_buffer.build().to_uint().value_or(1));
-            pager.top();
+                else
-        } else if (sequence == "G") {
+                    pager.down();
-            pager.bottom();
+            } else if (sequence == "k" || sequence == "\e[A") {
-        } else if (sequence == " " || sequence == "\e[6~") {
+                if (!emulate_more) {
-            pager.down_page();
+                    if (!modifier_buffer.is_empty())
-        } else if (sequence == "\e[5~") {
+                        pager.up_n(modifier_buffer.build().to_uint().value_or(1));
-            pager.up_page();
+                    else
+                        pager.up();
+                }
+            } else if (sequence == "g") {
+                if (!modifier_buffer.is_empty())
+                    pager.go_to_line(modifier_buffer.build().to_uint().value());
+                else
+                    pager.top();
+            } else if (sequence == "G") {
+                if (!modifier_buffer.is_empty())
+                    pager.go_to_line(modifier_buffer.build().to_uint().value());
+                else
+                    pager.bottom();
+            } else if (sequence == " " || sequence == "\e[6~") {
+                pager.down_page();
+            } else if (sequence == "\e[5~") {
+                pager.up_page();
+            } else if (sequence == "d") {
+                pager.down_half_page();
+            } else if (sequence == "u") {
+                pager.up_half_page();
+            }
+
+            modifier_buffer.clear();
         }
 
         if (quit_at_eof && pager.at_end())