Importing createVNode in tsx file

If you import createVNode, createFragment, createComponentVNode, createTextVNode, normalizeProps, etc. (not sure if this is the full list) in a tsx file, occurs an error.

For example, having createVNode imported in tsx file:
`Module parse failed: Identifier 'createVNode' has already been declared`

This probably happens because in updateSourceFile.ts imports for these functions are added without checking if they are already imported in the source file.