Support keypad-enter for text edit

[yasushima-gd]

keypad-enter will be enabled by this change.

In GLFW3, keypad-enter is GLFW_KEY_KP_ENTER.
But in the others environments, whether they are correct did not know.

[ocornut]

Thank you. I will look into it in the future.
In the meanwhile you can also assign io.KeyDown[ io.KeyMap[ImGuiKey_Enter] ] to be true when either of your key is true, in your implementation wrapper.

[ocornut]

@yasushima-gd I am dropping this PR.
As stated above it is easier if in your application to set io.KeyDown[io.KeyMap[ImGuiKey_Enter]] to be true when either key is true.

Keypad enum entries will probably be added eventually (particularly in relation to the Shortcut API requirements #456) but right now this isn't needed to achieve what you need, and I'll rather add all new enums together when we decide that will be needed.