Allow .. to be parsed as let initializer

.. and ..= are valid expressions, however when used in a let statement
it is not parsed.

src/test/ui/parser/issue-105634.rs

@@ -0,0 +1,8 @@
+// run-pass
+
+fn main() {
+    let _a = ..;
+    let _b = ..=10;
+    let _c = &..;
+    let _d = &..=10;
+}