Add infrastructure to build and publish as wasm32 (#3840)

Co-authored-by: Ingvar Stepanyan <me@rreverser.com>

docs/changelog.md

@@ -14,6 +14,9 @@ Requires libvips v8.15.0
 
 * Remove `sharp.vendor`.
 
+* Add experimental support for WebAssembly-based runtimes.
+  [@RReverser](https://github.com/RReverser)
+
 * Options for `trim` operation must be an Object, add new `lineArt` option.
   [#2363](https://github.com/lovell/sharp/issues/2363)
 

docs/humans.txt

@@ -278,3 +278,6 @@ GitHub: https://github.com/bianjunjie1981
 
 Name: Dennis Beatty
 GitHub: https://github.com/dnsbty
+
+Name: Ingvar Stepanyan
+GitHub: https://github.com/RReverser

docs/install.md

@@ -78,6 +78,15 @@ For cross-compiling, the `--platform`, `--arch` and `--libc` npm flags
 (or the `npm_config_platform`, `npm_config_arch` and `npm_config_libc` environment variables)
 can be used to configure the target environment.
 
+## WebAssembly
+
+Experimental support is provided for runtime environments that provide
+multi-threaded Wasm via Workers.
+
+```sh
+npm install --cpu=wasm32 sharp
+```
+
 ## FreeBSD
 
 The `vips` package must be installed before `npm install` is run.