Page modules: support for class variables

[FabienLelaquais]

Description

As of now (and Avaiga/taipy-gui#690), only instance variables can be reached by page definitions. Class variables are simply ignored.

Now in Python, a class variable really is a syntactic trick to define a global variable. You must know what class it is defined in to reach it, that's all.

It would be great to have Taipy GUI pages able to access class variables, and the broadcast mechanism applied to these so that they appear as global variables... in the scope of a given page, defined by a page module.

class MyPage(Page):
    shared_var = 0

    def __init__(self):
        self.var = 0
        super().__init__()

    def create_page(self):
        return Markdown("""
<|{var}|slider|>

<|{shared_var}|slider|>
""")
would work.

All clients would have their own value for the first slider, but moving the second one should update all clients.

**Acceptance Criteria**
- [ ] Ensure new code is unit tested, and check code coverage is at least 90%
- [ ] Ensure any change is well documented

[someshfengde]

Hi @jrobinAV can you please assign this issue to me?

[jrobinAV]

@someshfengde Thank you for your help.

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[Dkingofcode]

Hi @jrobinAV i would like to work on this issue. Although I am still a beginner in python it seems interesting, please i would like to ask if i can be given any resources that could be of help in solving this issue.

[github-actions[bot]]

This issue has been labelled as "🥶Waiting for contributor" because it has been inactive for more than 14 days. If you would like to continue working on this issue, please add another comment or create a PR that links to this issue. If a PR has already been created which refers to this issue, then you should explicitly mention this issue in the relevant PR. Otherwise, you will be unassigned in 14 days. For more information please refer to the contributing guidelines.