Update ECMASCRIPT.md

[smorimoto]

This may be a bit too much, but the current runtime dependencies are now truly exhaustive.

PR Overview

This PR updates ECMASCRIPT.md to document a more exhaustive list of runtime dependencies and ECMAScript features.

• Added several new feature sections (e.g., Arrow function expressions, const, for...of, let, WeakMap, BigInt, Optional chaining)
• Introduced new Web API compatibility sections (e.g., Canvas API, Crypto API, Document API)

Reviewed Changes

File	Description
ECMASCRIPT.md	Reorganized ECMAScript feature headings, added new features documentation, and introduced several Web API compatibility links.

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (3)

ECMASCRIPT.md:17

• The section heading was changed from 'Rest parameters' to 'const', but a 'Rest parameters' section appears later. Please verify if this reordering is intentional or if one of the headings needs to be corrected.

### const

ECMASCRIPT.md:11

• [nitpick] The note 'For Wasm_of_ocaml' appears repeatedly. Consider standardizing the formatting or clarifying its purpose to avoid redundancy.

- For Wasm_of_ocaml

ECMASCRIPT.md:55

• The change from a 'Map' section (which included a runtime usage note) to 'WeakMap' could be confusing. Please check if this replacement was intended or if both sections should coexist with clear descriptions.

### WeakMap