Improve YAML parsing error message

[cscheid]

Closes #9496.

[cscheid]

This is the new error message.

$ quarto render issue-9496.qmd
ERROR: YAML Parse Error: block has incorrect key formatting (issue-9496.qmd, 8:3)
 8: #| message: FALSE
 9: #| echo:false
       ~~~~~~~~~~
10: cat("HIIII")
ℹ Is it possible you missed a space after a colon in the key-value mapping?

Because I got thoroughly confused about our stack traces while debugging this issue, I also improved our stack trace printing debugging API so that it automatically highlights changes from one call to the next if called like getStack("ansi"). There's also getStack("json") if an array of objects is wanted for further processing.

Consecutive calls now look like this (actually slightly better; this screenshot has misaligned colons that are fixed in this PR):

[cscheid]

@cderv It's only an internal debugging aid right now. Add console.log(getStack("ansi"))