runtime(js): use es6 class

[smorimoto]

This PR updates several JavaScript runtime components to use ES6 class syntax instead of the traditional prototype-based object model. This modernization improves code readability and maintainability while aligning with current JavaScript best practices.

Changes

• Converted the classes to ES6 syntax
• Updated class inheritance patterns to use the extends keyword
• Replaced prototype method definitions with class methods
• Maintained all existing functionality while improving code structure

Benefits

• More readable and maintainable code structure
• Better alignment with modern JavaScript development practices
• Clearer class hierarchies through explicit extends relationships
• Improved code organization with methods contained within class definitions

Documentation

• Updated ECMASCRIPT.md to document ES6 class support

Testing

All existing tests continue to pass with the updated class implementations.

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[Copilot]

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

runtime/js/marshal.js:740

• [nitpick] Redeclaring the parameter 'pos' with 'var pos = pos;' is redundant and can be confusing; it is recommended to remove the redeclaration to use the parameter directly.

var pos = pos;

Copilot reviewed 5 out of 11 changed files in this pull request and generated no comments.

Files not reviewed (6)

• runtime/js/bigarray.js: Evaluated as low risk
• runtime/js/nat.js: Evaluated as low risk
• runtime/js/sync.js: Evaluated as low risk
• runtime/js/fs_fake.js: Evaluated as low risk
• runtime/js/int64.js: Evaluated as low risk
• runtime/js/fs_node.js: Evaluated as low risk

[smorimoto]

Related PR: #1846