check for creatable dependencies before generating alternate constructor

[davissuber]

Attempt to recreate the error case in #221

The key ingredient in this change is in ScopeImplFactory - before this change, the ScopeImpl output for the introduced test is:

package testcases.KT007_scope_factory_dependencies

import kotlin.Suppress
import motif.ScopeImpl

@Suppress("REDUNDANT_PROJECTION", "UNCHECKED_CAST")
@ScopeImpl(
  children = [],
  scope = Scope::class,
  dependencies = Scope.Dependencies::class,
)
public class ScopeImpl(
  private val dependencies: Scope.Dependencies,
) : Scope {
  public constructor() : this(object : Scope.Dependencies {})

  public fun scope(): Scope = this
}

Note that this does not compile because Scope.Dependencies has an abstract method.

[davissuber]

Not having an accessor for string() here is important otherwise the value of getDependencyMethodData(scope).isNotEmpty() in ScopeImplFactory will evaluate to true (which is why the test passed in the original pull request)

In other words, this pull request makes it possible to explicitly declare unused dependencies in motif.

[TonyTangAndroid]

I patched the diff and run the test and confirm that it works as expected. Thank you for your effort in fixing this long standing minor issue.