fix: restore diff highlighting in split-screen preview

[anatolytimonin]

This PR fixes an issue where syntax highlighting was not correctly applied in the diff preview when using a split-screen view. The changes ensure that the diff view is always properly highlighted, improving readability.

ISSUE #22

[FloppyDisco]

@anatolytimonin thank you so much for submitting this.

do you have any screen shots of this working?
it does not seem to pull up the files for me.

i'll look further into it as soon as i can!
thanks!

[dannypernik]

@FloppyDisco this seems to be working for me! Initially I had issues with cloning @anatolytimonin 's fork, though it might just be because I'm out of my element here. But I was able to manually apply the changes from the commit and create a vsix file. I now have the extension installed and working!

[FloppyDisco]

@dannypernik I'm glad to hear that!
I wasn't able to get it working. Maybe I didn't have everything updated correctly, I'll try again and see if I can publish the update if it works.

[FloppyDisco]

@anatolytimonin
i made the changes locally, because i was having trouble checking out your branch, but i'm merging this because i'd like you to get some credit here!
thanks!