RichLog fixes

[darrenburns]

• Fixes Initial RichLog width is wrong #4969
• Fixes RichLog shrink is shrinking renderable to min_width rather than the available width #4980
• Fixes width param in RichLog.write isn't respected #4981

Please review the following checklist.

• Docstrings on all new or modified functions / classes
• Updated documentation
• Updated CHANGELOG.md (where appropriate)

[darrenburns]

By deferring the initial render until the width is available, we can now render the content that was added via write in compose at the correct width, rather than doing the often wrong default of min_width.

[willmcgugan]

Apologies if you have considered this. Just catching up.

There is a danger here that if you defer writing that the renderable could change between the time you call write and the time it is rendered.

That shouldn't necessarily be a deal breaker. It is probably more surprising if a renderable doesn't fit.

Perhaps deferred writes should attempt to copy the renderable at the point of calling write?

[darrenburns]

I'd prefer to document that writes may be deferred until the widget is fully mounted rather than attempting copying, since renderables could be any object at all. They may not support copying or it may be expensive.

[darrenburns]

This shows the fix for width not being respected in write in action:

[darrenburns]

Previously, due to #4980, this would incorrectly shrink down to RichLog.min_width rather than the actual available content width.

[willmcgugan]

LGTM.

Suggest we copy Text renderables, since they have a copy method.