feat(shorebird_cli): Add OS wrapper for which/where.exe

[bryanoltman]

Description

Adds the OperatingSystemInterface class, which wraps OS-specific functionality (currently just which/where.exe for locating executables on a user's PATH).

Part of a solution for #1163 and #1213, which involves using the same logic as flutter to find these tools.

See https://github.com/flutter/flutter/blob/stable/packages/flutter_tools/lib/src/android/java.dart#L45-L54 for Java.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (5573939) 100.00% compared to head (6e9fb8b) 100.00%.
Report is 1 commits behind head on main.

❗ Current head 6e9fb8b differs from pull request most recent head 298ee66. Consider uploading reports for the commit 298ee66 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1403   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          156       157    +1     
  Lines         4633      4657   +24     
=========================================
+ Hits          4633      4657   +24     

Flag	Coverage Δ
shorebird_cli	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ird_cli/lib/src/os/operating_system_interface.dart	100.00% <100.00%> (ø)
packages/shorebird_cli/lib/src/process.dart	100.00% <100.00%> (ø)

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