Improve descriptions

Use struct declaration instead of struct to be more specific

Try to match TSPL conventions when discussing grammar

Remove semantic details

Author: andrewjl

CodeGeneration/Sources/SyntaxSupport/DeclNodes.swift

@@ -1823,7 +1823,7 @@ public let DECL_NODES: [Node] = [
           }
           ```
 
-          A struct can optionally declare no members.
+          A struct declaration may be declared without any members.
       """,
     kind: "Decl",
     traits: [
@@ -1836,51 +1836,51 @@ public let DECL_NODES: [Node] = [
         name: "Attributes",
         kind: .collection(kind: "AttributeList", collectionElementName: "Attribute"),
         nameForDiagnostics: "attributes",
-        description: "Attributes that are attached to the struct.",
+        description: "Attributes that are attached to the struct declaration.",
         isOptional: true
       ),
       Child(
         name: "Modifiers",
         kind: .collection(kind: "ModifierList", collectionElementName: "Modifier"),
         nameForDiagnostics: "modifiers",
-        description: "Modifiers that are attached to the struct.",
+        description: "Modifiers that are attached to the struct declaration.",
         isOptional: true
       ),
       Child(
         name: "StructKeyword",
         kind: .token(choices: [.keyword(text: "struct")]),
-        description: "The struct keyword."
+        description: "The struct declaration keyword."
       ),
       Child(
         name: "Identifier",
         kind: .token(choices: [.token(tokenKind: "IdentifierToken")]),
-        description: "The struct identifier."
+        description: "The struct declaration identifier. If the identifier matches a reserved keyword it must be enclosed in backticks."
       ),
       Child(
         name: "GenericParameterClause",
         kind: .node(kind: "GenericParameterClause"),
         nameForDiagnostics: "generic parameter clause",
-        description: "The generic parameters of the struct.",
+        description: "The generic parameters of the struct declaration.",
         isOptional: true
       ),
       Child(
         name: "InheritanceClause",
         kind: .node(kind: "TypeInheritanceClause"),
         nameForDiagnostics: "type inheritance clause",
-        description: "The inheritance clause of the struct type. This clause can contain only one or more protocols.",
+        description: "The struct declaration inheritance clause. It may contain one or more type identifiers.",
         isOptional: true
       ),
       Child(
         name: "GenericWhereClause",
         kind: .node(kind: "GenericWhereClause"),
         nameForDiagnostics: "generic where clause",
-        description: "The generic where clause of the struct",
+        description: "The generic where clause of the struct.",
         isOptional: true
       ),
       Child(
         name: "MemberBlock",
         kind: .node(kind: "MemberDeclBlock"),
-        description: "The members of the struct. Struct extensions may declare additional members so the contents of this block should not be assumed to be the complete member list for this struct."
+        description: "The members of the struct declaration. Because struct extension declarations may declare additional members the contents of this block may not always be the complete list of all members for this type."
       ),
     ]
   ),