Type composition is broken (embedded fields not detected)

It appears that embedded fields aren't being recognized by the parser, even if they have the appropriate `hcl` tag. This is a problem because that means I can't factor out common fields into a separate struct to avoid a bunch of copying and pasting when I only need a single optional label.

This is similar to https://github.com/hashicorp/hcl/issues/136, however the major difference here is that the embedded fields _are_ tagged. It does work if you add "remain", however that precludes you from mixing two structures into a third.

### Expectation

Given the following definition:

```go
type A struct {
A string `hcl:"a"`
}

type B struct {
A
B int `hcl:"b"`
}

type File struct {
Stuff []B `hcl:"stuff,block"`
}
```

This should load correctly

```hcl
stuff {
a = "asdf"
b = 123
}
```

### What Happens

Unfortunately, I get an error:
```
Error: test.hcl:3,3-4: Unsupported argument; An argument named "a" is not expected here.
```
If I comment out `a` then it works.

### Reproduction Example

```go
package main

import (
"fmt"

"github.com/hashicorp/hcl/v2/hclsimple"
)

type A struct {
A string `hcl:"a"`
}

type B struct {
A
B int `hcl:"b"`
}

type File struct {
Stuff []B `hcl:"stuff,block"`
}

func main() {
input := `
stuff {
a = "asdf"
b = 123
}
`

output := File{}
err := hclsimple.Decode("test.hcl", []byte(input), nil, &output)
fmt.Printf("Error: %v\n", err)
}
```

### Environment

OS: Ubuntu 22.04.1
Go: 1.19.4
hcl: v2.15.0

Start with hclsimple.Decode and the struct-tag handling used by the embedded-field reproduction. Add a regression test covering tagged embedded fields inside a block and verify that the sample HCL loads without reporting the embedded field as unsupported.

Written by the indexing model from the issue text.