Use namespaced Html class if available

[SomeMWDev]

This PR is made in reference to: #127

This PR addresses or contains:

• Fix compatibility with MW 1.44 by using the namespaced Html class if it is available.

This PR includes:

• Tests (unit/integration)
• CI build passed

Fixes #127

[SomeMWDev]

Tested on MW 1.39 and 1.45. This shouldn't break compatibility as it falls back to the non-namespaced Html class

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.78%. Comparing base (3725e29) to head (3a72826).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/MermaidParserFunction.php	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #131      +/-   ##
============================================
- Coverage     94.05%   92.78%   -1.28%     
- Complexity       24       25       +1     
============================================
  Files             5        5              
  Lines           101       97       -4     
============================================
- Hits             95       90       -5     
- Misses            6        7       +1     

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