Add colors to SCons error/warning messages

[Calinou]

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This also includes various improvements to the messages:

• Remove some "success" messages that were printed on every build, such as the macOS minimum supported version (which is already mentioned in the documentation. Only the "error" variants of these messages are kept.
• Use gray color for the build timer printed at the end of each build, and only display 2 decimals.
• Use non-zero exit codes when exiting after some error messages that previously exited with a zero (success) exit code.
• Improve formatting of the Direct3D 12 missing dependencies message.
• Clarify how MSVC is detected in the message printed when it's detected.
• Force colored output on CI (it's non-interactive but can still display colors).

Preview

I also had automatic underlining of backticked text at some point, but I removed it for now. Let me know if you'd like me to readd it: