Consider making `htmldocck` more specific

[jyn514]

Currently htmldocck allows the text in rustdoc tests to be shorter, but not longer than the expected test. So if the actual text were Option<T and you wrote Option<T>, it would fail the test. But if the actual were Option<T> and the expected were Option<T, it would pass the test.

This behavior is not super intuitive and seems like it could lead to false negatives where it didn't catch regressions. Rustdoc should consider changing it.

Originally posted by @jyn514 in #76934 (comment)