show exact data x and y values as cursor info in the histogram widget

[kswang1029]

Describe the bug
Currently the displayed cursor "x" value in the histogram widget is derived from the plot domain, not the data domain (ie display the xy values of the nearest data point). For practical usages, we should show the x value based on the data points.

Screen.Recording.2022-07-20.at.11.50.38.mov

To Reproduce
Steps to reproduce the behavior:

1. load an image and launch the histogram widget
2. move cursor around on the histogram plot and observe the displayed cursor values
3. y value is derived from the y value of the data point. This is correct.
4. x value is not derived from the x value of the data point. Instead, it is derived from the plot domain. This is the issue.

Expected behavior
Cursor info in the histogram widget should show values of the nearest data point.

Platform info (please complete the following information):

• OS [e.g. macOS Monterey]: macOS Monterey
• Browser [e.g. chrome, safari, electron app]: chrome
• Browser version [e.g. 22]: 103
• Backend branch [e.g. dev, v3b2 release]: dev
• Frontend branch [e.g. dev, v3b2 release]: dev