Update button.js

[rohitt05]

Reusability:
Added createIconPlaceholder() method to generate the placeholder icon. This avoids redundancy in the createEl method. Error Safety:

Added checks for this.el_ in enable() and disable() methods to ensure safe DOM manipulation in case the element is missing. Maintained All Code and Logic:

No existing logic was altered or omitted; all functionality is preserved. Optimized Comments:

Clarified comments to convey intent and removed redundant ones.

Description

Please describe the change as necessary.
If it's a feature or enhancement please be as detailed as possible.
If it's a bug fix, please link the issue that it fixes or describe the bug in as much detail.

Specific Changes proposed

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Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
  • Has no DOM changes which impact accessiblilty or trigger warnings (e.g. Chrome issues tab)
  • Has no changes to JSDoc which cause npm run docs:api to error
• Reviewed by Two Core Contributors

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