Add number and multiple choice field type icons

Purpose

Adds icons for number and multiple choice fields. A third field type, text, will be handled by an existing icon.

Closes #435 (closed)

Screenshots

hash	multiple-choice

Checklist

For a new icon and/or illustration:

• Link to related design issue: #435 (closed)
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.