[$200 in SQT] Improve error handling on Codegen for schema entities

[bz888]

Description

If an entity has a lowercase name it can result in invalid generated gode

// graphql.schema
type exampleField @entity {
 id: ID!
}

This will generate a fie ExampleField.ts However, the index.ts codegen will import exampleField.ts

The generated index.ts should have the correct case sensitive import