Update and cleanup of example project

[jamesncl]

Description

I couldn't build the example project using the latest versions of Android Studio and Flutter due to build errors, so I decided to do some upgrading, and while I was at it some additional cleanup. Here's a summary of changes:

• Upgraded gradle plugin for example android project
• Gitignore and remove auto-generated files from the demo Unity project to declutter and prevent potential problems (obj directory, .sln and .csproj files and others), using the ignores recommeded by unity
• Upgraded the demo Unity project to 2022.2.0 to match the officially supported version
• Fixed #784 and other build errors
• Removed 'Native Activity Demo' menu item from demo project which pointed to a non-existant route

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [x] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [x] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore

[jamesncl]

94643ed These changes to build.cs on master are ahead of the latest package, (made in #838)

I think it is better to update the package than delete the changes.

The only current difference in build.cs is avoiding an incorrect ios build, no new features.

As far as I know, the unitypackages are generated from the example project, the source isn't stored anywhere else.

Ah right, I didn't realise that - so in effect you're saying I have reverted to an earlier state of build.cs (compared to master)?

[timbotimbo]

Yes, you accidentally reverted build.cs to a version 1 commit earlier.

[jamesncl]

I'm going to close this pull request because I've made quite a big mistake (and learned a lot about how to do pull requests!) I've created this from the main branch of my own fork. What I should have done is made a separate branch first, and make the PR from that. Because I didn't do that, I can't progress in my own main branch without adding more commits to this PR. I'll close and make a new one soon.

[timbotimbo]

I like to create a separate branch and pull request per individual issue. This makes it easier for others to test only that specific change.

For example: changing the targetSdk and gradle versions is a good change, but you could easily separate that without upgrading the Unity project.

[jamesncl]

See my comment in another issue: I have implemented these changes in a brand new package