Reorganize library code into libs/

[encounter]

Splits library code into a separate libs/ structure:

libs
├── dolphin
│   ├── include
│   │   └── dolphin
│   └── src
│       ├── ai
│       ├── am
│       ├── amcnotstub
│       ├── amcstubs
|       └── ...
├── JSystem
│   ├── include
│   │   └── JSystem
│   └── src
│       ├── J2DGraph
│       ├── J3DGraphAnimator
│       ├── J3DGraphBase
|       └── ...
├── PowerPC_EABI_Support
│   ├── MetroTRK
│   ├── MSL
│   └── Runtime
│       ├── Inc
│       └── Src
├── revolution
│   ├── include
│   │   └── revolution
│   └── src
│       ├── ai
│       ├── aralt
│       ├── arc
│       ├── ax
|       └── ...
└── TRK_MINNOW_DOLPHIN
    ├── debugger
    └── gamedev

When building for GameCube, we only include libs/dolphin/includes. And for Wii/Switch, only libs/revolution/includes.

First commit only contains the file renames, and the second commit includes the changes made to configure.py and project.py.

Feel free to nitpick the structure and I can make any changes.

[decomp-dev]

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