hclwrite: add ObjectConsExpr.SetItemRaw() and ObjectConsExpr.ItemFor()

[bbasata]

Description

Rewrite object values.

config := []byte(`a = {
    hat = "derby", (cat) = "calico" }` + "\n")

bowler := hclwrite.TokensForValue(cty.StringVal(`bowler`))

file, _ := ParseConfig(config, "<inline>", hcl.Pos{})
attr := file.Body().GetAttribute("a")

expr := attr.Expr().AsObjectConsExpr()
key, value := expr.SetItemRaw("hat", bowler)

fmt.Printf("key: ")
key.BuildTokens(nil).WriteTo(os.Stdout)
fmt.Println()
fmt.Println("value: ")
value.BuildTokens(nil).WriteTo(os.Stdout)
fmt.Println()

Related Issue

#810