Add Khmer Digital - Khmer Unicode font family

Font Project Git Repo URL:
https://github.com/danhhong/khmerdigital

---

Super short description of the Font Family:

Khmer Digital is an official Khmer Unicode typeface released by the Ministry of Post and Telecommunications of Cambodia (MPTC), designed as a national standard font for digital government, enterprise systems, and public services. It provides a modern and highly readable design while preserving the integrity of Khmer typography.

---

By opening this issue, I confirm the project meets the following requirements:

- [x] The entire font project is available in a GitHub repository and licensed under the SIL Open Font License (OFL)
- [x] The source files are available in the repository
- [x] I am the copyright holder of the project, or all contributors have licensed their work under OFL
- [x] There are no Reserved Font Names conflicts
- [x] The font family name is unique
- [x] The naming is consistent across font files and metadata
- [x] The project follows the Google Fonts repository structure (/ofl/khmerdigital/)
- [x] The font includes multiple weights (Thin to Black)
- [x] The font supports Khmer Unicode and Latin characters
- [x] The project includes required files (METADATA.pb, DESCRIPTION, OFL, FONTLOG)
- [x] I have reviewed the Google Fonts contribution requirements
- [x] I am willing to maintain the project and participate in the review process

---

Additional details:

- The font family includes 9 weights (100–900)
- The font is optimized for government documents and digital services
- The font has been tested within Microsoft 365 environments (Word, Excel, Teams, SharePoint)
- The repository includes both TTF and WOFF2 formats for cross-platform usage
- This project is part of Cambodia’s national digital transformation initiative

---