feat: add GetWindowCompositionAttribute, SetWindowCompositionAttribute APIs

[halildurmus]

Description

Adds undocumented APIs to enable the "Aero Glass" blur effect on Win32 windows.

Related Issue

Fixes #934

Type of Change

• 🚀 feat – New feature (non-breaking change that adds functionality)
• 🛠️ fix – Bug fix (non-breaking change that fixes an issue)
• ❌ ! – Breaking change (fix or feature that causes existing functionality to change)
• ⚡ perf – Performance improvement
• 🧹 refactor – Code refactor (no functionality change)
• 📝 docs – Documentation update
• 🎨 style – Code style changes (formatting, renaming, etc.)
• 🧪 test – Test update or addition
• 🔧 build – Build related changes
• ✅ ci – CI related changes
• 🗑️ chore – Chore (maintenance, non-production code change)
• ◀️ revert – Revert a previous commit

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 61.80%. Comparing base (2eaeef1) to head (19c16d8).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/win32/lib/src/functions.dart	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #938      +/-   ##
==========================================
- Coverage   62.18%   61.80%   -0.38%     
==========================================
  Files          34       35       +1     
  Lines        1145     1152       +7     
==========================================
  Hits          712      712              
- Misses        433      440       +7     

Flag	Coverage Δ
win32	59.95% <0.00%> (-0.89%)	⬇️

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Files with missing lines	Coverage Δ
packages/win32/lib/src/constants.dart	6.66% <ø> (ø)
packages/win32/lib/src/enums.dart	66.66% <ø> (ø)
packages/win32/lib/src/functions.dart	0.00% <0.00%> (ø)