fix(shorebird_cli): verify that validators can be run before running them

[bryanoltman]

Description

Updates validatePreconditions to check that validators can be run before running them. If a validator that cannot be run in the current context is provided, prints an error message/usage instructions and exits.

Example:

Fixes #1253

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

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d12faa7) 98.93% compared to head (778ec6c) 98.93%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1254   +/-   ##
=======================================
  Coverage   98.93%   98.93%           
=======================================
  Files         179      179           
  Lines        4586     4590    +4     
=======================================
+ Hits         4537     4541    +4     
  Misses         49       49           

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 Changed	Coverage Δ
...idators/android_internet_permission_validator.dart	100.00% <ø> (ø)
...ib/src/validators/shorebird_flutter_validator.dart	100.00% <ø> (ø)
...ib/src/validators/shorebird_version_validator.dart	100.00% <ø> (ø)
...ges/shorebird_cli/lib/src/shorebird_validator.dart	100.00% <100.00%> (ø)
...s/shorebird_cli/lib/src/validators/validators.dart	100.00% <100.00%> (ø)

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[eseidel]

It's unclear to me from reading this what the affect on the user is.

e.g. is this trying to communicate a programmer error (we're executing code we didn't mean to some place) or user error (you're trying to do an unsupported thing)?

Is this validator only ever run for shorebird release android? Or is it also run for shorebird doctor?

Relatedly, do we handle using shorebird without an android directory at all? e.g. if you just wanted to use Shorebird on iOS?

[bryanoltman]

@eseidel added an example screenshot to the description.

It's unclear to me from reading this what the affect on the user is.

e.g. is this trying to communicate a programmer error (we're executing code we didn't mean to some place) or user error (you're trying to do an unsupported thing)?

A helpful error message will be printed instead of a crash when a user runs an android command in a Flutter app/module directory that does not have android support.

Is this validator only ever run for shorebird release android? Or is it also run for shorebird doctor?

Both. shorebird doctor will only attempt to run it if canRunInContext is true.

Relatedly, do we handle using shorebird without an android directory at all? e.g. if you just wanted to use Shorebird on iOS?

Yes (or we should and it's a bug that we don't). This validator only is only run on android-specific commands, so it should not be invoked for anything iOS-related.