[ui] NodeEditor: Don't allow to reduce split view size below 350

[cbentejac]

Description

This prevents reducing the Node Editor up to the point where components within it (especially in its header) are disappearing from screen.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.43%. Comparing base (08614a3) to head (bc91bab).
Report is 14 commits behind head on develop.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2699      +/-   ##
===========================================
+ Coverage    73.39%   73.43%   +0.04%     
===========================================
  Files          133      134       +1     
  Lines         7911     7924      +13     
===========================================
+ Hits          5806     5819      +13     
  Misses        2105     2105              

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