Refs: #10144

Following changes are included:

• consistently use monaco-monospace-font everywhere and define it for standalone editor too (via 2872e27)
• define a shared default font family for programmatic access and adopt it (via 05f2cec)
• define system-ui before Ubuntu but after Segoe (via ff69562 and 61214b5) to only change it for Linux distros unless they ship a Segoe font
• use the same font rules for different OS and languages in issue reporter and process explorer (via e49f99b)

Verification (Linux, Windows, macOS)

• overall workbench font
• process explorer
• issue reporter
• release notes (code blocks)