v2 log://log events are storing the Rust log::Level

Thanks for all the work around Tauri, v2 is amazing!
I noticed that there is a slight inconvenience around levels in the log plugin.

The plugin uses the following log level enum:
```js
export enum LogLevel {
Trace = 1,
Debug = 2,
Info = 3,
Warn = 4,
Error = 5,
}
```
.... while the enum in the log crate is flipped:
```rs
#[repr(usize)]
pub enum Level {
Error = 1,
Warn = 2,
Info = 3,
Debug = 4,
Trace = 5,
}
```

Now, it currently behaves a bit unintuitive when mixing webview logs with native logs.
When invoking the plugin command `plugin:log|log`, the handler is correctly mapping the webview level to the rust level.
However, events arriving in the webview at `log://log` are not mapped, so we currently have to map them back manually.

Since it's still the beta, wouldn't it make sense to not flip the enum order here and just use the log::LogLevel one?
If not, it would probably make sense to map levels arriving at `log://log` to the js ones.