Implement for_each and each.* extensions (#145)

This provides completion hints inside blocks for `for_each` and `each.*` references within `resource`, `data` and `module` blocks anywhere the `for_each` meta-argument is supported. It detects if `for_each` is used already and does not suggest duplicates and detects when it is necessary to provide `each.*` completions. This does not complete the values for `each.key` and `each.value`, e.g. `each.value.something`.

This also provides hover support for `for_each` and `each.*` references using the documentation as source.

This also provides semantic token support for `for_each` and `each.*` references.

Closes hashicorp/terraform-ls#861

Author: jpogran

decoder/body_candidates.go

@@ -26,6 +26,14 @@ func (d *PathDecoder) bodySchemaCandidates(body *hclsyntax.Body, schema *schema.
 				candidates.List = append(candidates.List, attributeSchemaToCandidate("count", countAttributeSchema(), editRng))
 			}
 		}
+
+		if schema.Extensions.ForEach {
+			// check if for_each attribute is already declared, so we don't
+			// suggest a duplicate
+			if _, present := body.Attributes["for_each"]; !present {
+				candidates.List = append(candidates.List, attributeSchemaToCandidate("for_each", forEachAttributeSchema(), editRng))
+			}
+		}
 	}
 
 	if len(schema.Attributes) > 0 {