test: rustdoc-ui: Add issue-74134, replacing test/rustdoc/issue-74134-*

As per the discussion in PR #74147, the 4 individual tests are replaced by a
single one.

The test is expanded to cover all 4 public/private cases, each with and without
--document-private-items.

src/test/rustdoc-ui/issue-74134.public.stderr

@@ -0,0 +1,10 @@
+warning: `[PrivateType]` public documentation for `public_item` links to a private item
+  --> $DIR/issue-74134.rs:19:10
+   |
+LL |     /// [`PrivateType`]
+   |          ^^^^^^^^^^^^^ this item is private
+   |
+   = note: `#[warn(intra_doc_link_resolution_failure)]` on by default
+
+warning: 1 warning emitted
+

src/test/rustdoc-ui/issue-74134.rs

@@ -0,0 +1,26 @@
+// revisions: public private
+// [private]compile-flags: --document-private-items
+// check-pass
+
+// There are 4 cases here:
+// 1. public item  -> public type:  no warning
+// 2. public item  -> private type: warning, if --document-private-items is not passed
+// 3. private item -> public type:  no warning
+// 4. private item -> private type: no warning
+// All 4 cases are tested with and without --document-private-items.
+//
+// Case 4 without --document-private-items is the one described in issue #74134.
+
+struct PrivateType;
+pub struct PublicType;
+
+pub struct Public {
+    /// [`PublicType`]
+    /// [`PrivateType`]
+    //[public]~^ WARNING `[PrivateType]` public documentation for `public_item` links to a private item
+    pub public_item: u32,
+
+    /// [`PublicType`]
+    /// [`PrivateType`]
+    private_item: u32,
+}