doc: improve assert.md regarding ECMAScript terms

Use the term "Abstract Equality Comparison" and "Strict Equality
Comparison" from ECMAScript specification to refer to the operations
done by `==` and `===`, instead of "equal comparison operator" and
"strict equality operator".

Clarify that deep strict comparisons checks `[[Prototype]]`
property, instead of the vague "object prototypes".

Suggest using `Object.is()` to avoid the caveats of +0, -0 and NaN.

Add a MDN link explaining what enumerable "own" properties are.

PR-URL: https://github.com/nodejs/node/pull/11128


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>