When converting documents containing Chinese, Japanese, or Korean
characters to PDF via pandoc/xelatex, the output was blank or missing
glyphs because no CJK-capable font was installed or configured.
Changes:
- Dockerfile: Add fonts-noto-cjk and texlive-lang-chinese packages
- pandoc.ts: Pass -V CJKmainfont=Noto Sans CJK SC to pandoc when
converting to pdf/latex, so xelatex uses a CJK-capable font
- pandoc.test.ts: Add 3 tests verifying CJK font argument is present
for pdf/latex output and absent for other formats
Fixes#547
