PLAT-10565 Adding utils classes

[symphony-mariacristina]

Ticket

PLAT-10565

Description

Adding some util classes on message processing to:

• Extract entities from a given incoming message (mentions, hashtags, cashtags, emojis)
• Extract message content from presentationML
• Pre-process an outgoing message by "cleaning" the text message, escaping all special characters that will violate messageML format
• Convert a stream id into a url safe id and viceversa

Checklist

• Referenced a ticket in the PR title and in the corresponding section
• Filled properly the description and dependencies, if any
• Unit tests updated or added
• Docstrings added or updated
• Updated the documentation in docs folder

[thibauult]

I need it in my current PR !! :)

[symphony-elias]

LGTM

[symphony-youness]

Curious question: Why do you call the parent constructor for Exception ?
.
.
On internet forums, the usual answer would be super().__init__ instead of Exception.__init__ as it would avoid us using the base class name explicitly.

I however don't see the point of calling the parent constructor if we set the instance attributes.
If you check the source code for Exception:

class Exception(BaseException):
    """ Common base class for all non-exit exceptions. """
    def __init__(self, *args, **kwargs): # real signature unknown
        pass

It only instanciates them for us. So my take would be droping the super().__init__ completly: https://docs.python.org/3.8/tutorial/errors.html -> 8.5. User-defined Exceptions

[symphony-mariacristina]

I updated these exceptions following the discussion on this page: https://stackoverflow.com/questions/2901000/the-correct-way-to-define-an-exception-in-python-without-pylint-complaining/2901085#290108 .
Pylint was complaining and raising warnings about it, so I followed this comment https://stackoverflow.com/a/2901085 and seems like Pylint is happy now.

But if there's a better way on how to handle this I'm open to change it.

[symphony-youness]

These discussions seem a bit old (dates of 2010), since python 3+, you would see things more like this: super().__init__: https://stackoverflow.com/questions/1319615/proper-way-to-declare-custom-exceptions-in-modern-python

I explained how I see things and how it was documented in the official documentation. Calling the parent constructor is not doing anything anyways which I think we should remove it.
https://docs.python.org/3.8/tutorial/errors.html -> 8.5. User-defined Exceptions

[symphony-youri]

if this error case can happen a lot maybe we would be better checking for it explictly (I don't know if it is similar to Java but exceptions have a performance cost and sometimes you want to avoid them)

[symphony-mariacristina]

The data object coming as payload from the message should be well formed in general. I put this block just to be safe that we are handling this scenario.