Fix the memory leak of FloatingLiteral/IntegerLiteral.

Fix the memory leak of FloatingLiteral/IntegerLiteral.

For large floats/integers, APFloat/APInt will allocate memory from the heap to represent these numbers.
Unfortunately, when we use a BumpPtrAllocator to allocate IntegerLiteral/FloatingLiteral nodes the memory associated with
the APFloat/APInt values will never get freed.
I introduce the class 'APNumericStorage' which uses ASTContext's allocator for memory allocation and is used internally by FloatingLiteral/IntegerLiteral.

Fixes rdar://7637185

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112361 91177308-0d34-0410-b5e6-96231b3b80d8