Inheritance for User-Defined Types

**Is your feature request related to a problem? Please describe.**

This feature request is not related to a problem I have, but more like an improvement on User-Defined Types (UDT). I am looking at UDTs like a class in TypeScript or C# for example. I know it's a different concept in Bicep, but it looks similar.

What would be great is to have the same concept of class inheritance in User-Defined Types. So, to have some kind of `base` type where other UDTs can `extend` or `inherit` from that base type.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

I will provide a practical example. In my recent PR in the Azure Verified Modules (https://github.com/Azure/bicep-registry-modules/pull/1931) repository I tried to achieve some kind of "inheritance" this way:

```bicep
type zoneBaseType = {
name: string
metadata: object?
ttl: int?
roleAssignments: roleAssignmentType
}
```

In the `zoneBaseType` UDT the base properties are defined that are used in every record type (a, aaaa, cname etc.) as seen below:

```bicep
type aType = {
@description('Required. The base properties of the record.')
base: zoneBaseType

targetResourceId: string?

aRecords: {
ipv4Address: string
}[]?
}[]?
```

The outcome is what I wanted, but not quite what I had in mind.

What would be great functionality to have is inheritance like we see in C# and TypeScript, so we can remove the need for a property like the `base: zoneBaseType` property.

How I see it with inheritance:

```bicep
type baseType = {
name: string
metadata: object?
ttl: int?
roleAssignments: roleAssignmentType
}

type aType extends baseType = {
targetResourceId: string?
aRecords: {
ipv4Address: string
}[]
}[]?
```

The type `aType` now extends from `baseType`, so when using the UDT `aType` you make use of the following properties:
* [inherited / extended from baseType] name: string
* [inherited / extended from baseType] metadata : object?
* [inherited / extended from baseType] ttl: int?
* [inherited / extended from baseType] roleAssignment: roleAssignmentType
* targetResourceId: string?
* aRecords: object

I hope this is clear and understandable. If not, please let me know.