Start the 1.2.0 release notes

[JeroenDeDauw]

Starts the release notes for 1.2.0, covering what has landed so far: syntax highlighting for fenced code blocks
(#37) and the code-block styling fix
(#36), both from
#41.

The heading says "Under development" rather than a date, so further entries can accumulate here before 1.2.0 is
released. No version bump: extension.json stays on 1.1.0 until the release commit, as in every release so far.

_{AI-authored — Claude Code, Fable 5 (max); asked by @JeroenDeDauw to reshape this from a release into release prep; one revision (was a Release 1.2.0 PR); diff not yet human-reviewed; release notes only, no code change.}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.25%. Comparing base (c0c6295) to head (4daea79).

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #42   +/-   ##
=========================================
  Coverage     83.25%   83.25%           
  Complexity      401      401           
=========================================
  Files            40       40           
  Lines          1039     1039           
=========================================
  Hits            865      865           
  Misses          174      174           

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