Add a test to detect overlapping entries in overview tables

Detects rust-lang#88545

Author: dns2utf8

src/test/rustdoc-gui/huge-collection-of-constants.goml

@@ -1,5 +1,4 @@
 goto: file://|DOC_PATH|/test_docs/huge_amount_of_consts/index.html
 
 // Make sure that the last two entries are more than 12 pixels apart and not stacked on each other.
-
 compare-elements-position-near-false: ("//*[@class='item-table']//div[last()-1]", "//*[@class='item-table']//div[last()-3]", {"y": 12})