Use .py3 extension to avoid clashes with built-in script provider.

[nneonneo]

There are actually useful scripts written in Jython with Python 2 syntax. It's very inconvenient to be unable to run these scripts with Ghidrathon installed. Upgrading existing scripts isn't completely straightforward either: for example, Jython supports shortcut syntax like obj.property instead of obj.getProperty() while JEP does not; never mind all of the little incompatibilities between Py2 and Py3.

This patch makes Ghidrathon only handle scripts with the .py3 extension. This only affects the script entry point; imported modules still use the .py extension as usual. Thus, the practical impact should be quite minimal. .py3 also serves to explicitly document that a script requires Ghidrathon to run.

With this patch, it is no longer necessary to disable the default script provider, and in fact you can use both Python 2 (Jython) scripts and Python 3 (Ghidrathon/JEP) scripts without any issues.

It's fairly straightforward to configure an editor to support .py3 just like .py. An alternative design would be to handle a double extension like .3.py, but that solution is uglier and will still require some kind of hack to prevent the existing script provider from handling them.

[nneonneo]

I'm aware this is an obvious breaking change, but I'm hoping that you're open to the change. The alternative is that Python 2 (Jython) scripts are simply unusable with the Ghidrathon extension installed, which isn't great. I imagine that even if Ghidra ever gains a Python 3 interpreter, there will still need to be some mechanism to distinguish Python 2 scripts from Python 3 scripts for compatibility with existing scripts.

[ryanmkurtz]

As of Ghidra 11.2, the proper way to avoid clashes is to extend AbstractPythonScriptProvider, override getRuntimeEnvironmentName() to return something like Ghidrathon, and use the @runtime Ghidrathon tag in your scripts. This allows multiple providers to share the same file extension.