Docs: Relocate the content of NOTE documents

[nick-y-ito]

Overview

This PR relocates the content of ICON_NOTE.md and removes STYLE_NOTE.md with additional refactoring.

Changes

• Move the Steps to use an icon of ICON_NOTE.md to the Icon.tsx as TSDocs.
• Refactor the Icon.tsx file
• Move the Steps to create a new icon section to STYLEGUIDE.md.
• Delete the STYLE_NOTE.md because the content was stale and we no longer needed it.
• Rename the Icon components in src/assets/images/icons/index.ts.

Review points

Although there are many files that have been changed, you only need to review the following files:

• docs/STYLEGUIDE.md
• src/assets/images/icons/index.ts
• src/components/ui/Icon.tsx
• tailwind.config.ts

Notes

Assignee Checklist:

• [x] The naming convention of the PR title is correct (See the comment at the top of this template)
• [x] The base branch is correct (See: Types of Branches)
• [x] The branch name follows the Branch Naming Conventions
• [x] The correct assignees and reviewers have been designated for this PR
• [x] The coding style follows the Coding Style Guide
• [x] All the related issues are associated with this PR
• [x] All criteria in the associated issues are met (please tick the checkboxes)
• [x] My changes do not generate new warnings or errors (especially in the console)

Reviewer Checklist:

• [ ] Double-check the "Assignee Checklist"
• [ ] The code follows the generic best practices and our Coding Style Guide
• [ ] The code is well-commented and easy to understand
• [ ] The UI changes accurately reflect the provided design

[nick-y-ito]

@kanta1207 Thank you for your review :)