Add build time generated math using Katex embedded as WASI

[bep]

While very useful on its own (and combined with the passthrough render hooks), this also serves as a proof of concept of using WASI (WebAssembly System Interface) modules in Hugo.

This will be marked experimental in the documentation. Not because it will be removed or changed in a dramatic way, but we need to think a little more how to best set up/configure similar services, define where these WASM files gets stored, maybe we can allow user provided WASM files plugins via Hugo Modules mounts etc.

See these issues for more context:

• transform.ToMath, WASI/Wasm modules feedback thread #12736
• Further ideas on how WASI/Wasm modules could be used in Hugo #12737

[bep]

We would need a fix for tetratelabs/wazero#2294 for this to go beyond a proof of concept, I think, but I'm working on it.

[bep]

OK, my upstream Wazero patch was just merged (!). I'm going to do finish the "render hook" part of this in #12717 first, and then return to this PR.

[bep]

transform.ToMath(opts any)

Where opts is converted to KatexInput:

type KatexInput struct {
	Expression string       `json:"expression"`
	Options    KatexOptions `json:"options"`
}

type KatexOptions struct {
	Output      string `json:"output"` // html, mathml (default), htmlAndMathml
	DisplayMode bool   `json:"displayMode"`
}

There may be some more (https://katex.org/docs/options.html) useful end user option, but it's not obvious to me.

Does the func signature above make sense, @jmooring ?

[jmooring]

Does the func signature above make sense?

I'm sure you have a good reason for the signature above, but I would have expected this instead:

{{ $expression := "c = \\pm\\sqrt{a^2 + b^2}" }}
{{ $opts := dict "output" "mathml" "displaymode" true }}
{{ $result := transform.ToMathML $expression $opts }}

where $opts has reasonable defaults (e.g., output = mathml, displaymode = true).

[bep]

I'm sure you have a good reason for the signature above, but I would have expected this instead:

Only me being lazy, I guess. So, from an end users perspective I guess it makes sense to have them split, so options can be defined somewhere (e.g. in hugo.toml). I'll fix that.

[bep]

{{ $result := transform.ToMathML $expression $opts }}

Also note that I have named it transform.ToMath (there are some different ossible output formats, not just mathml).

[bep]

OK, I have pushed a verion of transform.ToMath with 2 args, the last (options) optional.