[base/properties]Cache values of AliasProperty where possible

[pythonic64]

Builds upon #5856 and aims to increase widgets performance by caching values of AliasProperty where possible.

[pythonic64]

For case in kivy/uix/screenmanager.py I think we need another method in AliasProperty, like recache() which will call getter function and update the cache with new value or recache_and_dispatch() which will also dispatch the new value if it has changed.

[pythonic64]

@tshirtman @KeyWeeUsr Can you take a look at this pull request?

[pythonic64]

@tito What do you think about adding a recache method to AliasProperty?

[tito]

@pythonic64 What rebase would do in your mind?

Anyway, just another couple of changes here and it would be ok.

[tito]

Just remove the couple of caching discussed in command and we're good to merge!

[pythonic64]

@tito I didn't mentioned any rebasing, but I did ask about recache method:

@tito What do you think about adding a recache method to AliasProperty?

I think it should be added just to have a way to explicitly cache value returned by getter method of AliasProperty.

[pythonic64]

Request should be good to merge now. I will investigate TextInput._lines_flags attribute to see if it can be changed to ListProperty and then we can use it to cache text property.

[matham]

Please let us know when you think it's in a good state to merge.

[pythonic64]

@matham @tito You can merge this now.

Changes implemented

[matham]

Seems to have implemented @tito 's changes so it looks ok.