Add tomoki1207.pdf

[greyscaled]

👋, To the best of my knowledge, I'm following etiquette for getting https://github.com/tomoki1207/vscode-pdfviewer into Open VSX.

• The repository's last commit was a few months ago, so I take it that the repo is maintained
• There was an issue opened a year prior to the latest commit about Open VSX here: Publish extension on open vsx tomoki1207/vscode-pdfviewer#89
• The package.json seems like it meets the criteria here for not needing additional build steps
• The extension has id tomoki1207.pdf (pasted from here: https://marketplace.visualstudio.com/items?itemName=tomoki1207.pdf)
• The repo has an MIT LICENSE

• I have read the note above about PRs contributing or fixing extensions
• I have tried reaching out to the extension maintainers about publishing this extension to OpenVSX (if not, please create an issue in the extension's repo using this template).
• This extension has an OSI-approved OSS license (we don't accept proprietary extensions in this repository)

Description

This PR introduces adding tomoki1207.pdf change to add it to Open VSX. The extension does not seem unmaintained, but the issue for adding it to OpenVSX has not been responded to: tomoki1207/vscode-pdfviewer#89.

[filiptronicek]

LGTM, thanks for the PR ✅