Allow custom ID for a subplot

[remss]

Hello Implot-Team! Currently each plot of a subplot will have a PushID with its index. There should be a way to set a custom value for this. In my case I have options to show/hide/reorder subplot items and therefore the same plotted metric ends with a different ID path depending of the user choice. When the user changes the layout then the plot state is lost because its ID path has changed.

[remss]

Here is a sample repro case where the state is lost. I create a subplots of 2 plots P1 and P2, I zoom/pan P2 then I remove P1 to display only P2. Then you see the P2 has lost its state and the zoom/pan is reset.

int cols = 0;
static auto sinLamda = [](int idx, void *f) { return ImPlotPoint(idx, sinf(idx * (*(float *)f))); };
static bool showP1 = true;
ImGui::Checkbox("Show P1", &showP1);
if (showP1)
{
    cols++;
}
static bool showP2 = true;
ImGui::Checkbox("Show P2", &showP2);
if (showP2)
{
    cols++;
}
ImPlotSubplotFlags flags = 0;
if (ImPlot::BeginSubplots("Test Subplots", 1, cols, ImVec2(0, 0), flags))
{
    if (showP1)
    {
        if (ImPlot::BeginPlot("p1"))
        {
            static float f1 = 0.3f;
            ImPlot::PlotLineG("v", sinLamda, &f1, 100);
            ImPlot::EndPlot();
        }
    }
    if (showP2)
    {
        if (ImPlot::BeginPlot("p2"))
        {
            static float f2 = 0.1f;
            ImPlot::PlotLineG("v", sinLamda, &f2, 100);
            ImPlot::EndPlot();
        }
    }
    ImPlot::EndSubplots();
}

[epezent]

Hi! I think we can support this by adding a new subplot flag, e.g. ImPlotSubplotFlags_NoAutoID, which would disable the internal ID push/pop and place the responsibility on the user. Thoughts?

[remss]

It's ok for me thanks!