Write a PyCharm plugin

### What is the problem or limitation you are having?

There are two main issues:
1. I hope to add build plugins that PyCharm can use instead of using CMD to build, as PyCharm is more efficient in writing code.
2. I hope to remove the code templates related to the platform from the build directory, as it is usually necessary to add the build directory to the .gitignore file. If the code templates are also excluded, it will result in modifications to the code templates that cannot be managed by VCS. For example, I need to modify the Android template and add some third-party dependency libraries to the build.gradle file. As there are relatively few existing Python libraries available for mobile devices, I need to use some third-party jars to expand the functionality and use rubicon-java to call in the Python layer.

### Describe the solution you'd like

1. I hope to add a build plugin for PyCharm.
2. I hope to modify the storage directory of the code template.

### Describe alternatives you've considered

There is currently no solution for the first problem;
The second issue can be implemented using the sub module of Git, but it is not elegant enough, and the build directory often needs to be cleaned, so I will not choose this solution either.

### Additional context

See #1451 for an equivalent request for VSCode.

Start by reviewing how Briefcase currently handles the build directory and code templates, then compare the equivalent VSCode request in #1451. Define the scope for PyCharm build-plugin support and a separate template storage location; done means both requested workflows are supported without losing template changes to build-directory cleanup.

Written by the indexing model from the issue text.