Table of Contents contains too much

[joyously]

Looking at a Code Reference page for a function, like ​https://developer.wordpress.org/reference/functions/get_extended/
the table of Contents in the sidebar has a link to "Logged in as x. Log out?" and more text from the instructions about leaving feedback, which are not links, and don't belong there.

It looks like the plugin looking at more than the_content.

[joyously]

the extra stuff is in the sidebar at the bottom of CONTENTS

[joyously]

I just noticed that there are two sections at the bottom that are almost the same, for adding feedback. That extra might be where the ToC plugin is getting it from.

[dd32]

In 11354:

Handbooks, ToC: Be less greedy when matching headings within the content.

[11341] didn't change the greedyness, but as it was now matching headings with attributes, it was matching too much on reference pages.

Additionally, we now don't use style-only headings (those without text) as valid sections.

See #5963.
Fixes #5973.