Fix BiDi bug with mixed explicit dir in paragraph (#3532)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

crates/typst/src/layout/inline/mod.rs

@@ -432,6 +432,8 @@ fn collect<'a>(
         segments.push((Segment::Spacing((-hang).into()), *styles));
     }
 
+    let outer_dir = TextElem::dir_in(*styles);
+
     while let Some(mut child) = iter.next() {
         let outer = styles;
         let mut styles = *styles;
@@ -445,11 +447,26 @@ fn collect<'a>(
             Segment::Text(1)
         } else if let Some(elem) = child.to_packed::<TextElem>() {
             let prev = full.len();
+            let dir = TextElem::dir_in(styles);
+            if dir != outer_dir {
+                // Insert "Explicit Directional Isolate".
+                match dir {
+                    Dir::LTR => full.push('\u{2066}'),
+                    Dir::RTL => full.push('\u{2067}'),
+                    _ => {}
+                }
+            }
+
             if let Some(case) = TextElem::case_in(styles) {
                 full.push_str(&case.apply(elem.text()));
             } else {
                 full.push_str(elem.text());
             }
+
+            if dir != outer_dir {
+                // Insert "Pop Directional Isolate".
+                full.push('\u{2069}');
+            }
             Segment::Text(full.len() - prev)
         } else if let Some(elem) = child.to_packed::<HElem>() {
             if elem.amount().is_zero() {

tests/typ/layout/par-bidi.typ

@@ -47,6 +47,13 @@ Lריווח #h(1cm) R
 // Test whether L1 whitespace resetting destroys stuff.
 الغالب #h(70pt) ن#" "ة
 
+---
+// Test explicit dir
+#set text(dir: rtl)
+#text("8:00 - 9:00",dir:ltr) בבוקר
+#linebreak()
+ב #text("12:00 - 13:00",dir:ltr) בצהריים
+
 ---
 // Test setting a vertical direction.
 // Ref: false