[CODE-DOC] replace attribute=Component.UNDEFINED by default values

[MM-Lehmann]

When displaying the inline code documentation, it is very hard to read through all those Component.UNDEFINED attribute defaults. Could we not replace those by their default values or None? At least with a repr() of some kind?
Or is this just me with PyCharm?

[chriddyp]

We can't actually use None or default values because explicitly providing None is different than not providing any value at all. For context, see this PR that introduced Component.UNDEFINED: #276