Remove the dedicated `zig build lib-vt` step and replace it with a
`-Demit-lib-vt` build option. This fixes two problems:
1. We can default XCFramework, app, etc. steps to false if emit-lib-vt
is true, so that the lib-vt build doesn't pull in unrelated
artifacts. **Most importantly, lib-vt alone can be build without
full Xcode installations.**
2. We can build lib-vt as part of a bundle with other artifacts if we
really want.
This adds a set of Wasm convenience functions to ease memory management.
These are all prefixed with `ghostty_wasm` and are documented as part of
the standard Doxygen docs.
I also added a very simple single-page HTML example that demonstrates
how to use the Wasm module for key encoding.
This also adds a bunch of safety checks to the C API to verify that
valid values are actually passed to the function. This is an easy to hit
bug.
**AI disclosure:** The example is AI-written with Amp. I read through
all the code and understand it but I can't claim there isn't a better
way, I'm far from a JS expert. It is simple and works currently though.
Happy to see improvements if anyone wants to contribute.
