One-click guest profiler results

#### Feature

When invoking the guest profiler via either its `GuestProfiler` Rust API or the Wasmtime CLI, we should provide the option of running a local web server to serve profile data, then generating links to https://profiler.firefox.com/ that direct it to load the profile data directly from the local web server.

#### Benefit

Currently, we write the profile data to a file, then tell the user the path to that file. They then browse to https://profiler.firefox.com/ and use their browser's file-open dialog to find the path we told them. It would be more convenient to give them a single URL which automatically loads the profile data.

Running a local web server also allows us to symbolicate lazily and serve source code to the viewer on-demand, in principle.

#### Implementation

The Samply profiler illustrates how to do this, in https://github.com/mstange/samply/blob/main/samply/src/server.rs.

#### Alternatives

We could continue just writing the profile to a file and letting the user find it in their filesystem.

I was hesitant to suggest doing this in Wasmtime before because it means we need to depend on an HTTP server like `hyper`. I thought it would be better to implement the parts which depend on a web server in embedders such as Viceroy that have their own web server. But now that we've implemented wasi-http, Wasmtime depends on `hyper` anyway, so we might as well do it in Wasmtime where it can be shared across multiple embedders.