[ROSIDL] Add toPlainObject() method for array messages

[minggangw]

This patch adds support for converting array messages to plain objects by introducing a helper function to detect typed arrays and updating relevant tests.

Fix: #1046

PR Overview

This PR adds support for converting array messages to plain objects by introducing a helper function to detect typed arrays and updating relevant tests.

• Added an isTypedArray helper in utils.js.
• Updated tests to import the centralized isTypedArray helper.
• Modified test-message-properties-validation.js to call toPlainObject with the enableTypedArray flag.

Reviewed Changes

File	Description
test/utils.js	Added isTypedArray utility function and exported it.
test/test-message-properties-validation.js	Updated the toPlainObject call to pass enableTypedArray flag.
test/test-message-translator-primitive.js	Replaced local isTypedArray definition with import from utils.js.
test/test-array-data.js	Replaced local isTypedArray definition with import from utils.js.
test/test-message-translator-complex.js	Removed local isTypedArray definition in favor of the shared one.

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test/test-message-properties-validation.js:181

• The updated usage of toPlainObject with the enableTypedArray flag consolidates the conversion logic for both plain objects and array messages, but it removes the per-element conversion previously applied to ROS arrays. Please verify that the new behavior produces the correct plain object representation for array messages.

left[i].toPlainObject(/*enableTypedArray=*/ true)