Implement a LateInitializer struct for use by providers

[muvaf]

Description of your changes

LateInitializer will help providers figure out whether a change has been made and spec update is needed after the late initialization without using DeepCopy of the original and changed objects.

I wanted to include only the bare minimum I need for generated ACK resources where the source and target field types are the same to be conservative about what we expose. We can add more as needed.

Example usage:

func lateInitialize(cr *svcapitypes.Table, resp *svcsdk.DescribeTableOutput) bool {
  li := awsclients.NewLateInitializer()
  cr.Spec.ForProvider.Property = li.LateInitializeStringPtr(cr.Spec.ForProvider.Property, resp.Table.Property)
  // .. many calls using the same li object ...
  return li.IsChanged()
}

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Unit tests.

[hasheddan]

@muvaf this looks good to me! One thing I was considering is whether we should add a SetChanged() method in case someone is using this with an unsupported type, but don't want to track if any changes happen in a separate variable, any thoughts on that?

[muvaf]

@hasheddan sounds good. I started with having a lot of LateInitialize* functions and then reduced to these few, thinking providers could extend it if they want non-conventional late initialize functions but missed the fact that they can't access changed field. Thanks!