Change materialx.emoji.twemoji to material.extensions.emoji.twemoji

[atteggiani]

Connected to #706

Context

mkdocs-material module materialx.emoji.twemoji was changed to material.extensions.emoji.twemoji in this issue that was merged in this PR.

As a consequence, the deployment log shows the following deprecation warning:

INFO    -  DeprecationWarning: 'materialx.emoji.twemoji' is deprecated.
Material emoji logic has been officially moved into mkdocs-material
version 9.4. Please use Material's 'material.extensions.emoji.twemoji'
instead of 'materialx.emoji.twemoji' in your 'mkdocs.yml' file.

Actions to close issue

• Change all the instances of materialx.emoji to material.extensions.emoji in the mkdocs.yml file.