Repeated config arguments results in a confusing error

I am unsure if this belongs here or over in https://github.com/yargs/yargs instead, but I think it's mostly an issue here in the parser.

In any case, I went and wrote a little CLI tool using nodejs and yargs and in particular its .config() mechanism; so far, so good. However, if I pass --config more than once (e.g. --config a.json --config b.json), it dies with the help message and the confusing report Invalid JSON config file: [ './a.json', './b.json' ]. A little brute force shows that that report arises from https://github.com/yargs/yargs-parser/blob/217aa62906d0bbd40e06d675b8a23df8d49a5ad4/lib/yargs-parser.ts#L688 but is, ultimately, because the call to mixin.resolve on https://github.com/yargs/yargs-parser/blob/217aa62906d0bbd40e06d675b8a23df8d49a5ad4/lib/yargs-parser.ts#L666 is, by default, a call to path.resolve (owing to https://github.com/yargs/yargs-parser/blob/90f970a6482dd4f5b5eb18d38596dd6f02d73edf/lib/index.ts#L38) and path.resolve balks if not given a string as its second argument.

At the very least the error could be more informative (perhaps, "configuration options may be given at most once"), but because it's possible to have multiple .config() directives applied to yargs, and so the machinery tolerates the notion of multiple config files in general, I would prefer to wrap the entirety of https://github.com/yargs/yargs-parser/blob/217aa62906d0bbd40e06d675b8a23df8d49a5ad4/lib/yargs-parser.ts#L664-L689 in a loop to handle the case that configPath is an array.

Reproduce the repeated --config case, then inspect lib/yargs-parser.ts around lines 664-689 and the default resolver in lib/index.ts around line 38. Determine whether array-valued config paths should be handled or rejected with a clearer message, and verify the resulting behavior with the parser's existing tests.