create separated module for meta struct (according to development protocol)

src/browser/main/tab/page/meta.rs

@@ -0,0 +1,26 @@
+use gtk::glib::GString;
+use std::cell::RefCell;
+
+pub enum Mime {
+    Undefined,
+    TextGemini,
+    TextPlain,
+}
+
+pub struct Meta {
+    pub title: GString,
+    pub description: GString,
+    pub mime: Mime,
+    pub progress_fraction: f32,
+}
+
+impl Meta {
+    pub fn new() -> RefCell<Meta> {
+        RefCell::new(Self {
+            title: GString::new(),
+            description: GString::new(),
+            mime: Mime::Undefined,
+            progress_fraction: 0.0,
+        })
+    }
+}