Add regression test for issue 53820

Author: Nadrieril

src/test/ui/pattern/issue-53820-slice-pattern-large-array.rs

@@ -0,0 +1,10 @@
+// check-pass
+#![feature(slice_patterns)]
+
+fn main() {
+    const LARGE_SIZE: usize = 1024 * 1024;
+    let [..] = [0u8; LARGE_SIZE];
+    match [0u8; LARGE_SIZE] {
+        [..] => {}
+    }
+}