implement view-source feature

src/app/browser/window/tab/item/page/content/text/source.rs

@@ -0,0 +1,25 @@
+use gtk::{TextBuffer, TextView};
+
+const MARGIN: i32 = 8;
+
+pub struct Source {
+    pub text_view: TextView,
+}
+
+impl Source {
+    pub fn new(data: &str) -> Self {
+        Self {
+            text_view: TextView::builder()
+                .bottom_margin(MARGIN)
+                .buffer(&TextBuffer::builder().text(data).build())
+                .cursor_visible(false)
+                .editable(false)
+                .left_margin(MARGIN)
+                .monospace(true)
+                .right_margin(MARGIN)
+                .top_margin(MARGIN)
+                .vexpand(true)
+                .build(),
+        }
+    }
+}