Fix invalid HTML in "should allow html entities" tooltip unit test

Refs #14090.
Also, fix one typo.
Merge pull request #14091 from twbs/tooltip-test-html-fix

Fix unusual HTML in "should allow html entities" tooltip unit test
Fix IE8 reporting height style as all uppercase
Fix IE8 reporting type object for `getBoundingClientRect`
`document.head` is undefined in IE8