Fix ImGuiIO docs and default values

[Endilll]

ImGuiIO doc and constructor body seem to be out of sync a bit.
Maybe we should go one step further and eliminate the duplication by providing default initializers directly in struct declaration?

[ocornut]

Thanks for the PR.

On DisplaySize and Fonts, I think the existing comments are more in line with the information we want to convey in that header. A display size needs to be set, and atlas is auto-created on context creation if not provided. So there's only 1 miss-sync of value here, and the two false initializers are not strictly necessary but better to have them for consistency and searchability.

Maybe we should go one step further and eliminate the duplication by providing default initializers directly in struct declaration?

I agree but would need to carefully check with VS version does that limit us to. (see #4537)

[ocornut]

Based on https://docs.microsoft.com/en-us/cpp/overview/visual-cpp-language-conformance?view=msvc-160

C++11 Everything else | VS 2015
N3653 Default member initializers for aggregates | VS 2017 15.0
P0683R1 Default member initializers for bit-fields | VS 2019 16.5

Based on that I don't think we should use them for aggregate nor bit-fields and I worry this would create quite a bunch of inconsistencies in some structures, but probably good enough for ImGuiIO only.