fix: Embeds subtitle on saved screenshots

[WongChoice]

Fixes #1898

I would like to claim the bounty offered.

What does this PR do?

Adds the feature which embeds subtitle inheriting the subtitle customization from the extension.

Following is the example

[ImprovedTube]

hi @WongChoice thank you so much!

• we can split this into two functions, so we can also append the subtitle to the end of the file name (said in Can the screenshot function display subtitles in the screenshot? #1898).
  • (the we can also add a sub-feature to make the caption on the screenshot optional, both groups of users might exist)

bounty

are you avaiable for more work? maybe send an email? whats your hourly rate?

• i just started using the label #bounty experimentally & we currently receive no donations, yet we should & thats the point, and i can pay some bounties myself to start with...

thanks!

[WongChoice]

Hi thank you for merge
thank you so much for bothering to ask.
I would have really appreciated a pay.
At present i have my interests inclined toward ML. Please feel free to point me to any PR in future. thanks