Add a regression test for public struct field spans

Author: chellmuth

src/test/compile-fail/pub-struct-field-span-26083.rs

@@ -0,0 +1,20 @@
+// Regression test for issue #26083
+// Test that span for public struct fields start at `pub` instead of the identifier
+
+struct Foo {
+    pub bar: u8,
+
+    pub
+    //~^ error: field `bar` is already declared [E0124]
+    bar: u8,
+
+    pub bar:
+    //~^ error: field `bar` is already declared [E0124]
+    u8,
+
+    bar:
+    //~^ error: field `bar` is already declared [E0124]
+    u8,
+}
+
+fn main() { }