Adds override for face org-block to avoid a region within the block begin indistinguishable from the block's background. Uses face base2 for org-block{-background,-begin-line]}.

Theme doom-theme-monokai-pro was not included since it doesn't have this problem.

• themes/doom-monokai-classic-theme.el
• themes/doom-monokai-machine-theme.el
• themes/doom-monokai-octagon-theme.el
• themes/doom-monokai-ristretto-theme.el
• themes/doom-monokai-spectrum-theme.el

Fix: #762

• I searched the issue tracker and this hasn't been PRed before.
• My changes are not on the do-not-PR list for this project.
• My commits conform to the git conventions.
• My changes are visual; I've included before and after screenshots.
• Any relevant issues or PRs have been linked to.
• This a draft PR; I need more time to finish it.

Screenshot

Using doom-monokai-machine as an example.

Before

After