Improve API configuration update() error message

[joaomoreno]

Testing #31448

I attempted to write to a non-resource setting from an extension, under the folder scope. I got this error:

Shouldn't the error be more specific? Something in the lines of:

The xxx setting can't be set under the yyy configuration target because zzz.

Something like that?

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Related to #31541 due to wording

[joaomoreno]

Similarly, I'm now trying to update a setting on the WorkspaceFolder target, but I scope to a resource which isn't contained by any of the open folders. I get the same generic message:

It should describe why I can't do what I'm trying to do.

[sandy081]

Yah this is how we had been reporting for invalid configuration target. Good that we discover such old issues (with wordings) too.