[Exploration] Split into monorepo with 17 npm workspace packages

[brnrdog]

The current single-package @rescript/webapi bundles all Web API bindings together, which creates
significant overhead for consumers who only need a subset of the APIs. By splitting into independent
packages, we:

• Decrease the overhead/overload of the Web API — consumers install and compile only the bindings
  they actually use
• Decrease compilation time — smaller dependency graphs mean faster builds for projects that
  don't need every API surface

Summary

• Reorganize the single @rescript/webapi package into a monorepo with npm workspaces and 17
  independent packages
• All type definitions stay in the base @rescript/webapi package; binding packages depend only on
  the base, eliminating circular dependencies
• Each package builds independently and consumers can install only what they need

Package structure

@rescript/webapi (base types + Event + tiny modules — 77 files)
├── @rescript/webapi-dom (122 files)
├── @rescript/webapi-fetch (8 files)
├── @rescript/webapi-file (12 files)
├── @rescript/webapi-canvas (7 files)
├── @rescript/webapi-webaudio (31 files)
├── @rescript/webapi-uievents (14 files)
├── @rescript/webapi-web-workers (4 files)
│   └── @rescript/webapi-service-worker (12 files)
├── @rescript/webapi-indexed-db (5 files)
├── @rescript/webapi-media (8 files)
├── @rescript/webapi-websockets (3 files)
├── @rescript/webapi-geolocation (3 files)
├── @rescript/webapi-webstorage (2 files)
├── @rescript/webapi-crypto (2 files)
├── @rescript/webapi-performance (3 files)
└── @rescript/webapi-global (1 file)

Key changes

• Created packages/ directory with 17 packages, each with package.json and rescript.json
• Moved 314 .res files from flat src/ into flattened package src/ directories
• Updated open statements in type definition files (open Event → open EventTypes, open File →
  open FileTypes) to reference type modules directly
• Fixed cross-package module references in DOM, Fetch, Canvas, UIEvents, WebSockets, and Global
• Moved IntersectionObserverRoot.res to webapi-dom (depends on DOM bindings)
• Inlined File.isInstanceOf in FormDataEntryValue.res to avoid circular package dependency
• Added -open WebAPIWebWorkers to service-worker config for WorkerGlobalScope.Impl
• Replaced deprecated bsc-flags with compiler-flags across all packages
• Updated test files for new namespace paths
• Added build / clean scripts to all packages and build:packages to root

Build scripts

npm run build            # build everything from root
npm run build:packages   # build each package independently
npm run clean            # clean all build artifacts
npm run build -w @rescript/webapi-dom  # build a single package

Test plan

• npm run clean && npm run build — all 336 modules compile from clean build
• npm run build:packages — each of the 17 packages builds independently
• Verify a sample consumer project can depend on individual packages

[brnrdog]

Closing this one in favour of #249