decoder: Add support for TypeDeclaration as Constraint (#183)

* Introduce PathContext to TypeDeclaration

This is required in order to recover bytes of incomplete configuration during completion.

* decoder: Implement completion for TypeDeclaration

* decoder: Implement hover for TypeDeclaration

* add tests

---------

Co-authored-by: James Pogran <jpogran@outlook.com>

decoder/expr_type_declaration.go

@@ -1,29 +1,16 @@
 package decoder
 
 import (
-	"context"
-
-	"github.com/hashicorp/hcl-lang/lang"
 	"github.com/hashicorp/hcl-lang/schema"
 	"github.com/hashicorp/hcl/v2"
 )
 
 type TypeDeclaration struct {
-	expr hcl.Expression
-	cons schema.TypeDeclaration
-}
-
-func (td TypeDeclaration) CompletionAtPos(ctx context.Context, pos hcl.Pos) []lang.Candidate {
-	// TODO
-	return nil
-}
-
-func (td TypeDeclaration) HoverAtPos(ctx context.Context, pos hcl.Pos) *lang.HoverData {
-	// TODO
-	return nil
+	expr    hcl.Expression
+	cons    schema.TypeDeclaration
+	pathCtx *PathContext
 }
 
-func (td TypeDeclaration) SemanticTokens(ctx context.Context) []lang.SemanticToken {
-	// TODO
-	return nil
+func isTypeNameWithElementOnly(name string) bool {
+	return name == "list" || name == "set" || name == "map"
 }