HTML escape should accept only string and null

[mvorisek]

#3222 fixes missing number.replace function well, but null type is converted to "null". "" is mostly wanted to be displayed instead.

undefined is converted to "undefined". But most undefined cases are handled explicitly and values passed using setting.someValue should always be defined. Thus do not have to handle this case in general.

Casting object or array types using String() is bad and should never be done.

[mvorisek]

This PR addresses #3222 (comment).

Refs:

• https://stackoverflow.com/questions/12594683/how-to-force-a-string-value-in-html-5-data-attributes
• https://github.com/fomantic/Fomantic-UI/blob/2.9.4/src/definitions/modules/dropdown.js#L2905

This behaviour is sadly caused by https://github.com/jquery/jquery/blob/3.7.1/src/data.js#L24-L47. This is impossible to be fully fixed in Fomantic-UI JS without patching jQuery on the page load (prior any jQuery operations).

See related atk4/ui#2274 / atk4/ui@45d47a9.