Added PlotBubbles

[Luc16]

Summary
This PR adds support for bubble plots to ImPlot, inspired by MATLAB’s bubblechart. Existing plot functionality is unaffected.

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Function signatures

IMPLOT_TMP void PlotBubbles(const char* label_id, const T* values, const T* szs, int count, double xscale=1, double xstart=0, ImPlotBubblesFlags flags=0, float min_pxsize=3, float max_pxsize=50, int offset=0, int stride=sizeof(T));

IMPLOT_TMP void PlotBubbles(const char* label_id, const T* xs, const T* ys, const T* szs, int count, ImPlotBubblesFlags flags=0, float min_pxsize=3, float max_pxsize=50, int offset=0, int stride=sizeof(T));

IMPLOT_API void PlotBubblesG(const char* label_id, ImPlotGetter3D getter, void* data, int count, ImPlotBubblesFlags flags=0, float min_pxsize=3, float max_pxsize=50);

• min_pxsize and max_pxsize set the minimum and maximum bubble diameters (in pixels).
• By default, marker outlines are not rendered and the fill color alpha is set to 0.5.

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Example
Below is an example bubble plot (two different datasets). The bubble sizes are scaled between the specified min_pxsize and max_pxsize ([3, 50] for blue and [5, 20] for orange):

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Feedback
Please let me know if there are any suggestions or improvements regarding:

• The API signature or naming.
• Default styling choices (e.g., alpha, line rendering).
• Performance or edge-case handling.

I appreciate any comments or reviews on how to refine this feature!