[SyntaxTree][Nit] Take `ArrayRef` instead of `std::vector` as argument for `createTree`

[eduucaldas]

Summary

I also assured that there are no other functions unnecessarily using std::vector as argument.

clang/include/clang/Tooling/Syntax/BuildTree.h

 /// this token
 syntax::Leaf *createLeaf(syntax::Arena &A, tok::TokenKind K);
 
 // Synthesis of Trees
 /// Creates the concrete syntax node according to the specified `NodeKind` `K`.
 /// Returns it as a pointer to the base class `Tree`.
 syntax::Tree *
 createTree(syntax::Arena &A,
-           std::vector<std::pair<syntax::Node *, syntax::NodeRole>> Children,
+           ArrayRef<std::pair<syntax::Node *, syntax::NodeRole>> Children,
            syntax::NodeKind K);
 
 // Synthesis of Syntax Nodes
 syntax::EmptyStatement *createEmptyStatement(syntax::Arena &A);
 
 /// Creates a completely independent copy of `N` (a deep copy).
 ///
 /// The copy is:

clang/lib/Tooling/Syntax/Synthesis.cpp

case syntax::NodeKind::ParameterDeclarationList:
     return new (A.getAllocator()) syntax::ParameterDeclarationList;
   }
   llvm_unreachable("unknown node kind");
 }
 } // namespace
 
 syntax::Tree *clang::syntax::createTree(
     syntax::Arena &A,
-    std::vector<std::pair<syntax::Node *, syntax::NodeRole>> Children,
+    ArrayRef<std::pair<syntax::Node *, syntax::NodeRole>> Children,
     syntax::NodeKind K) {
   auto *T = allocateTree(A, K);
   FactoryImpl::setCanModify(T);
   for (auto ChildIt = Children.rbegin(); ChildIt != Children.rend(); ++ChildIt)
     FactoryImpl::prependChildLowLevel(T, ChildIt->first, ChildIt->second);
 
   T->assertInvariants();
   return T;