restructure: move el compiler content into lang/

lang/tests/text/examples/index-of-all.el

@@ -0,0 +1,21 @@
+// index-of-all.el — every byte offset of a substring.
+// "abXcdXefX" / "X" -> [2, 5, 8]. Empty list when no matches.
+fn run_test() -> String {
+    let positions: [Int] = str_index_of_all("abXcdXefX", "X")
+    let n: Int = native_list_len(positions)
+    let out: String = ""
+    let i: Int = 0
+    while i < n {
+        let p: Int = native_list_get(positions, i)
+        if i > 0 {
+            let out = out + ","
+        }
+        let out = out + int_to_str(p)
+        let i = i + 1
+    }
+    return out
+}
+
+fn main() -> Void {
+    println(run_test())
+}