warn when fig.path is shared among different knitr documents

[cscheid]

If fig.path is shared among different knitr documents in a book, freeze behaves very strangely.

We should probably disallow freeze: true and fig.path being both set at the same time.

[cderv]

I need to look into that.

fig.path will always be set by rmarkdown so by Quarto too.

I guess we are talking about value set by user directly ?

There is an expectation with fig.path value in Quarto it seems, which is the R Markdown default.
And I think this means it can't be modified by users inside a project document.

For reference, default path will be <input>_files/figure-<format>

and I am quite sure this is not expected to be changed... Probably more than just a freeze problem when I see

quarto-cli/src/core/render.ts

Lines 13 to 16 in 1995444

	export function inputFilesDir(input: string) {
	const [_, stem] = dirAndStem(input);
	return stem + "_files";
	}

I will think about making this option non-modifiable maybe in quarto context.

Knowing the reason of this configuration could be useful. This is in quarto a knitr only configuration I believe, just because it is a supported knitr option.