This PR adds a platform for WebAssembly. Heavily inspired by Pavel's
QemuUser, the platform lets you configure a WebAssembly runtime to run a
Wasm binary.
For example, the following configuration can be used to launch binaries
under the WebAssembly Micro Runtime (WARM):
```
settings set -- platform.plugin.wasm.runtime-args --heap-size=1048576
settings set -- platform.plugin.wasm.port-arg -g=127.0.0.1:
settings set -- platform.plugin.wasm.runtime-path /path/to/iwasm-2.4.0
```
With the settings above, you can now launch a binary directly under
WAMR:
```
❯ lldb simple.wasm
(lldb) target create "/Users/jonas/wasm-micro-runtime/product-mini/platforms/darwin/build/simple.wasm"
Current executable set to '/Users/jonas/wasm-micro-runtime/product-mini/platforms/darwin/build/simple.wasm' (wasm32).
(lldb) b main
Breakpoint 1: 2 locations.
(lldb) r
Process 1 launched: '/Users/jonas/wasm-micro-runtime/product-mini/platforms/darwin/build/simple.wasm' (wasm32)
2 locations added to breakpoint 1
[22:28:05:124 - 16FE27000]: control thread of debug object 0x1005e9020 start
[22:28:05:124 - 16FE27000]: Debug server listening on 127.0.0.1:49170
the module name is /Users/jonas/wasm-micro-runtime/product-mini/platforms/darwin/build/simple.wasm
Process 1 stopped
* thread #1, name = 'nobody', stop reason = breakpoint 1.3
frame #0: 0x40000000000001d3 simple.wasm`main at simple.c:8:7
5 }
6
7 int main() {
-> 8 int i = 1;
9 int j = 2;
10 return add(i, j);
11 }
(lldb)
```
