Fix #14224: Correctly document args passed to function vals for `title` & `content` options of tooltips+popovers
Fix #14219: Document that empty tooltips+popovers do not get displayed
Merge pull request #14257 from twbs/fix-14219

Document that empty tooltips+popovers do not get displayed
Merge pull request #14256 from twbs/fix-14224

Correctly doc args passed to function vals for `title` & `content` options of tooltips+popovers
Document arguments passed to `placement` function of tooltip/popover

Closes #14255