[Outreachy Task Submission] Add Hidden Button Value Text for main-filter toggle btn in Map and Data Screens

[Chiemezuo]

Introduction

The "main-filter toggle" button icon in both the Data and Map views has a problem. The button has only an icon and has no value text. While this is just a stylistic choice, it raises an issue with any accessibility checking tool. It does this because a button having no value text is a violation of WCAG Success Criterion 1.1.1 (Level A) - Non-text content. See. See a screenshot of the pertinent component:

Note the SVG icon

How to Test the PR

Manually Testing

1. Open your browser and log into your running Ushahidi deployment (from localhost).
2. Navigate to either the data or map section.
3. Try right-clicking on the arrow by the side of the navigation and selecting 'inspect'.
4. View the properties. Notice you won't see any button value text.
5. You will not see any text in it.
6. Stop the running Ushahidi deployment in your terminal.
7. Checkout to this PR branch.
8. Re-run your Ushahidi deployment.
9. Repeat steps 1-3.
10. You will see a value in the buttton element this time around, and this text will be visually hidden.

Using an Accessibility Checker

If you use a tool like WAVE evaluation tool, it's as simple as following steps 1 and 2 above, and then turning on the browser extension. It will flag the issue. Checkout to the PR and do this again, you will notice the issue is no longer flagged.

Dependency

This fix has a dependency on a previous PR

Fixes

This fixes #4905