Fix-76141 Add border around image in image preview

[skprabhanjan]

@mjbvz , Added the border property accordingly to fix #76141 and kept it default as I could not find the panel color that was mentioned in this comment

I will change it if you can provide me the color code.

This is how it looks for default border 1px solid

[dbaeumer]

@bpasero FYI. Could be you as well :-)

[mjbvz]

Thanks @skprabhanjan.

We probably want to use a border color from one of our existing theme colors, such as panel.border perhaps. Adding @aeschli for ideas on which theme color to use.

Here's an example of how write a style that uses a theme color:

vscode/src/vs/workbench/contrib/terminal/browser/terminalPanel.ts

Line 332 in 982e7bc

const backgroundColor = theme.getColor(TERMINAL_BACKGROUND_COLOR);

Just add a call to registerThemingParticipant in resourceViewer and then move the css border rule into a string within it

[aeschli]

reusing panel.border is not really 100% proper, but fine with me. You could also add a new color: imagePreview.border

[skprabhanjan]

@mjbvz and @aeschli
Added imagePreview.border which has same values as panel.border and used that in registerThemingParticipant in resourceViewer .
Please check and review this :)

PS : This is how it looks now.

[mjbvz]

Thanks! This will be in the next VS Code 1.37 insiders build and is scheduled to go out in the July release