refactor: establish DOM core folder

[jderochervlk]

Tracking issue: #342

Stack context

Part 1 of the Option 5 folder-feature stack.

• Previous: refactor: move CSS and stylesheets out of DOM #288
• Next: refactor: establish Event folder feature #312 (Event folder feature)

Review this PR as the incremental diff against #288. It begins the structural stack after the flat interface/type extraction is complete.

Summary

• rename src/Base to the target src/core folder
• move EventType.res into core beside the foundational event types in DOM.res
• make the internal DOM feature include the complete core folder
• simplify WebAPI.DOM to imply only the DOM folder feature
• remove the one-file EventType feature slice and the exclusion required by the Event folder

Public module paths remain WebAPI.DOM and WebAPI.EventType.

Temporary state

• the legacy BaseFile, BaseFileAndDirectoryEntries, BaseCSSFontLoading, and BaseEncryptedMediaExtensions helpers remain in core for now; later File, CSSFontLoading, and Media layers will move or replace them in their owning folders
• the existing broad src/DOM source entry is still tagged as WebAPI.DOM; later DOM platform/node, HTML, Window, CSSOM, Geometry, SVG, Animation, Navigator, and Canvas layers will split it into unqualified folder features
• because of that legacy source entry, the qualified public WebAPI.DOM selective build is not yet the final light bundle; the internal DOM folder feature itself compiles independently in this layer

Review focus

• whether EventType belongs in the foundational core needed by DOM.EventListener
• removal of the module-slice exception without changing public module names
• preservation of source behavior across the folder rename

Verification

• node_modules/.bin/rescript clean
• node_modules/.bin/rescript build --prod --features DOM
• npm run build
• npm test
• npm run format:check
• git diff --check

[jderochervlk]

@codex

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. You're on a roll.

Reviewed commit: 571359f038

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".