Fix aria-pressed initialization for toggle buttons

[puneetdixit200]

Description

Initializes missing aria-pressed on button plugin instances from the current .active state. Inactive toggle buttons now get aria-pressed="false", and already-active toggle buttons get aria-pressed="true" when the attribute was not present in the markup.

Motivation & Context

Fixes #42328.

The button plugin already keeps aria-pressed in sync when toggling. This covers the initial state so assistive technologies can identify the button as a toggle before the first click.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (npm run js-lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Tests

• Red check: npm_config_cache=/tmp/bootstrap-42328-npm-cache npm run js-test-karma failed before the implementation with the new test seeing aria-pressed as null.
• Green check: npm_config_cache=/tmp/bootstrap-42328-npm-cache npm run js-test-karma reported 810/810 successful tests and exited 0. Karma also printed its existing full-page-reload shutdown warning.
• npm_config_cache=/tmp/bootstrap-42328-npm-cache npm run js-lint exited 0, with existing warning-comment warnings in unrelated files.
• git diff --check

AI assistance was used for implementation and verification. I reviewed the code and test results before submitting.