Consider modifying validation to account for duplicate names used in attributes and blocks

Within the [terraform-plugin-codegen-framework](https://github.com/hashicorp/terraform-plugin-codegen-framework/pulls), models are generated from the [specification](https://github.com/hashicorp/terraform-plugin-codegen-spec/blob/main/spec/specification.go). Currently, it is possible for the specification to contain names that are duplicated across attributes and blocks. For instance, the following intermediate representation is currently permitted

```json
{
{
"datasources": [
{
"name": "datasource",
"schema": {
"attributes": [
{
"name": "one",
}
],
"blocks": [
{
"name": "one",
```

This results in the generation of a valid schema with the following form:

```go
datasourceDataSourceSchema = schema.Schema{
Attributes: map[string]schema.Attribute{
"one": /*...*/
},
Blocks: map[string]schema.Block{
"one": /*...*/
},
}
```

However, it also results in the generation of an invalid model with the following form:

```go
type DatasourceModel struct {
One types.Bool `tfsdk:"one"`
One types.List `tfsdk:"one"`
}
```