C: Parser: Support parsing of c99 designated initializers

In case:

    int a[6] = { [4] = 29, [2] = 15 };
    struct point { int x, y; };
    struct point p = { .y = 3, .x = 2 };

Grammar change when c99 language feature is enabled:
old grammar:

    braced-init-list :: '{' initializer-list '}'

new grammar:

    braced-init-list :: '{' designated-initializer-list '}'
    designated-initializer-list :: designated-initializer (',' designated-initializer )*
    designated-initializer :: designator* initializer-clause
    designator :: '.' identifier
                | '[' constant-expression ']'

Task-number: QTCREATORBUG-1902
Change-Id: Ib99d6f553f8d0f50ba3eff86f3a2e86d73372426
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/libs/3rdparty/cplusplus/AST.cpp

@@ -4450,3 +4450,69 @@ unsigned AliasDeclarationAST::lastToken() const
     return 1;
 }
 
+/** \generated */
+unsigned DesignatedInitializerAST::firstToken() const
+{
+    if (designator_list)
+        if (unsigned candidate = designator_list->firstToken())
+            return candidate;
+    if (equal_token)
+        return equal_token;
+    if (initializer)
+        if (unsigned candidate = initializer->firstToken())
+            return candidate;
+    return 0;
+}
+
+/** \generated */
+unsigned DesignatedInitializerAST::lastToken() const
+{
+    if (initializer)
+        if (unsigned candidate = initializer->lastToken())
+            return candidate;
+    if (equal_token)
+        return equal_token + 1;
+    if (designator_list)
+        if (unsigned candidate = designator_list->lastToken())
+            return candidate;
+    return 1;
+}
+
+unsigned DesignatorAST::firstToken() const
+{
+    if (type == DesignatorAST::Dot) {
+        if (u.dot.dot_token)
+            return u.dot.dot_token;
+        if (u.dot.identifier_token)
+            return u.dot.identifier_token;
+    } else if (type == DesignatorAST::Bracket) {
+        if (u.bracket.lbracket_token)
+            return u.bracket.lbracket_token;
+        if (u.bracket.expression)
+            if (unsigned candidate = u.bracket.expression->firstToken())
+                return candidate;
+        if (u.bracket.rbracket_token)
+            return u.bracket.rbracket_token;
+    }
+    return 0;
+}
+
+unsigned DesignatorAST::lastToken() const
+{
+    if (type == DesignatorAST::Dot) {
+        if (u.dot.identifier_token)
+            return u.dot.identifier_token + 1;
+        if (u.dot.dot_token)
+            return u.dot.dot_token + 1;
+    } else if (type == DesignatorAST::Bracket) {
+        if (u.bracket.rbracket_token)
+            return u.bracket.rbracket_token + 1;
+        if (u.bracket.expression)
+            if (unsigned candidate = u.bracket.expression->lastToken())
+                return candidate;
+        if (u.bracket.lbracket_token)
+            return u.bracket.lbracket_token + 1;
+    }
+    return 1;
+}
+