v1.5.0 doesn't understand that Transform is Fn::Transform

[pbudzon]

CloudFormation Lint Version

1.5.0

What operating system are you using?

Mac

Describe the bug

We're trying to move from v0 of cfn-lint to v1, but the current v1.5.0 immediately blows up with the following when trying to run it against our templates (v0 works just fine).
We using Transform at top-level of our templates, but cfn-lint doesn't seem to understand it is the same as Fn::Transform and throws nonsensical errors.

If Transform is given a list, cfn-lint immediately fails with:

ValueError: Transform must be a string

That error message makes no sense, because Transform can be a string OR an array. Which is confirmed by this next error - see below.

If Transform is given an array, cfn-lint throws E1001:

E1001 {'Name': 'SomeMacro', 'Parameters': {'SomeParam': 'something'}} is not of type 'string', 'array'

Which also makes no sense, because that object is indeed an array.

If we replace Transform with Fn::Transform cfn-lint works as expected. Both versions are valid and work correctly with CloudFormation.

Expected behavior

cfn-lint should treat Transform and Fn::Transform the same in situations where they are valid yaml. Or at least show better error messages if treating them the same is not possible.

Reproduction template

Template with a list, that fails with ValueError:

AWSTemplateFormatVersion: "2010-09-09"
Description: Example

Transform:
  - Name: SomeMacro
    Parameters:
      SomeParam: something

Resources:
  SillyParameter:
    Type: AWS::SSM::Parameter
    Properties:
      DataType: text
      Type: String
      Value: abc

Template with single macro, so Transform gets an array:

AWSTemplateFormatVersion: "2010-09-09"
Description: Example

Transform:
  Name: SomeMacro
  Parameters:
    SomeParam: something

Resources:
  SillyParameter:
    Type: AWS::SSM::Parameter
    Properties:
      DataType: text
      Type: String
      Value: abc

[kddejong]

Adding support as we can. Also tagging #476 which discusses the general need of Transform support.