[docs] Update docs since getBasicBlockList() is now private

llvm/docs/ProgrammersManual.rst

 * ``bool isDeclaration()``
 
   Return whether or not the ``Function`` has a body defined.  If the function is
   "external", it does not have a body, and thus must be resolved by linking with
   a function defined in a different translation unit.
 
 * | ``Function::iterator`` - Typedef for basic block list iterator
   | ``Function::const_iterator`` - Typedef for const_iterator.
-  | ``begin()``, ``end()``, ``size()``, ``empty()``
+  | ``begin()``, ``end()``, ``size()``, ``empty()``, ``insert()``,
+    ``splice()``, ``erase()``
 
   These are forwarding methods that make it easy to access the contents of a
   ``Function`` object's BasicBlock_ list.
 
-* ``Function::BasicBlockListType &getBasicBlockList()``
-
-  Returns the list of BasicBlock_\ s.  This is necessary to use when you need to
-  update the list or perform a complex action that doesn't have a forwarding
-  method.
-
 * | ``Function::arg_iterator`` - Typedef for the argument list iterator
   | ``Function::const_arg_iterator`` - Typedef for const_iterator.
   | ``arg_begin()``, ``arg_end()``, ``arg_size()``, ``arg_empty()``
 
   These are forwarding methods that make it easy to access the contents of a
   ``Function`` object's Argument_ list.
 
 * ``Function::ArgumentListType &getArgumentList()``

llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl05.rst

 emitting into if, for example, it contains a nested "if/then/else"
 expression. Because calling ``codegen()`` recursively could arbitrarily change
 the notion of the current block, we are required to get an up-to-date
 value for code that will set up the Phi node.
 
 .. code-block:: c++
 
       // Emit else block.
-      TheFunction->getBasicBlockList().push_back(ElseBB);
+      TheFunction->insert(TheFunction->end(), ElseBB);
       Builder.SetInsertPoint(ElseBB);
 
       Value *ElseV = Else->codegen();
       if (!ElseV)
         return nullptr;
 
       Builder.CreateBr(MergeBB);
       // codegen of 'Else' can change the current block, update ElseBB for the PHI.
       ElseBB = Builder.GetInsertBlock();
 
 Code generation for the 'else' block is basically identical to codegen
 for the 'then' block. The only significant difference is the first line,
 which adds the 'else' block to the function. Recall previously that the
 'else' block was created, but not added to the function. Now that the
 'then' and 'else' blocks are emitted, we can finish up with the merge
 code:
 
 .. code-block:: c++
 
       // Emit merge block.
-      TheFunction->getBasicBlockList().push_back(MergeBB);
+      TheFunction->insert(TheFunction->end(), MergeBB);
       Builder.SetInsertPoint(MergeBB);
       PHINode *PN =
         Builder.CreatePHI(Type::getDoubleTy(TheContext), 2, "iftmp");
 
       PN->addIncoming(ThenV, ThenBB);
       PN->addIncoming(ElseV, ElseBB);
       return PN;
     }