Move rustdoc tests to appropriate subdirectories

Reorganize rustdoc tests into their correct subdirectories for better
categorization:
- Move lint-related tests to rustdoc-ui/lints/
- Move intra-doc link tests to rustdoc-ui/intra-doc/
- Move deref-related tests to rustdoc-ui/deref/
- Move doc-cfg test to rustdoc/doc-cfg/

This improves test organization and makes it easier to find tests
related to specific rustdoc functionality.

tests/rustdoc-ui/lints/include-str-bare-urls.rs

@@ -12,6 +12,6 @@
 // If the stderr file changes, make sure the warning points at the URL!
 
 #![deny(rustdoc::bare_urls)]
-#![doc=include_str!("auxiliary/include-str-bare-urls.md")]
+#![doc=include_str!("../auxiliary/include-str-bare-urls.md")]
 
 //~? ERROR this URL is not a hyperlink

tests/rustdoc-ui/lints/include-str-bare-urls.stderr

@@ -1,5 +1,5 @@
 error: this URL is not a hyperlink
-  --> $DIR/auxiliary/include-str-bare-urls.md:1:11
+  --> $DIR/../auxiliary/include-str-bare-urls.md:1:11
    |
 LL | HEADS UP! https://example.com MUST SHOW UP IN THE STDERR FILE!
    |           ^^^^^^^^^^^^^^^^^^^

tests/rustdoc-ui/lints/remap-path-prefix-lint.stderr

@@ -1,11 +1,11 @@
 error: unopened HTML tag `script`
-  --> remapped_path/remap-path-prefix-lint.rs:9:5
+  --> remapped_path/lints/remap-path-prefix-lint.rs:9:5
    |
 LL | /// </script>
    |     ^^^^^^^^^
    |
 note: the lint level is defined here
-  --> remapped_path/remap-path-prefix-lint.rs:7:9
+  --> remapped_path/lints/remap-path-prefix-lint.rs:7:9
    |
 LL | #![deny(rustdoc::invalid_html_tags)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^