feat: merge a11y changes from sumac into teak branch

[DawoudSheraz]

Merge the following PR changes into teak/indigo so that a11y fixups become part of v4.

• Toggle the theme on pressing the enter key #27 – Toggle theme using keyboard Enter key
• fix: Add visible titles to image-based links #28 – Add visible titles to image-based links
• feat: enhance accessibility by adding descriptive label to theme toggle #29 – Feat: enhance accessibility by adding a descriptive label to the theme toggle
• feat: Header - Focus order meaning - Open Edx Demo Course #30 - Header - Focus order meaning - Open Edx Demo Course

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.58%. Comparing base (38d2651) to head (73b1a5d).
Report is 1 commits behind head on teak/indigo.

Files with missing lines	Patch %	Lines
src/ThemeToggleButton.jsx	88.88%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           teak/indigo      #32      +/-   ##
===============================================
+ Coverage        64.77%   68.58%   +3.80%     
===============================================
  Files               49       49              
  Lines              477      487      +10     
  Branches           106      110       +4     
===============================================
+ Hits               309      334      +25     
+ Misses             165      150      -15     
  Partials             3        3              

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