Pending docs changes (addon.* API)

[WorldLanguages]

#7376

• addon.self.lib no longer exists
• Add addon.self.dynamicImport It's going to get removed
• Add to best practices: use former method instead of raw import()
• addon.tab.loadScript now takes a relative URL instead of an absolute one. (Relative to chrome-extension://id/, not to the current file)

#7386

• The window.addon = addon debugging tip is no longer needed as __addon will usually work in the console. This tip could be added in other places as well, such as addon API documentation

Missing best practices:

• Avoiding mousemove and similar DOM events that trigger too often
• When polluting a method, first check if other addons that do the same, and consider conflicts & race-conditions
• Take advantage of addon.tab.scratchMsg() instead of creating our own strings, when appropriate

Unsure if it belongs in any page:

• Generally, enabling a setting changes vanilla Scratch behavior, not the other way

[Hans5958]

PS. Could you start reviewing #323?

[Samq64]

Generally, enabling a setting changes vanilla Scratch behavior, not the other way

We should probably add a UX page at some point.