[BUG] [typescript-fetch] uniqueItems in query params does not work

[Nikos410]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

If uniqueItems is true for an array, the typescript-fetch generator uses a Set instead of an array. This does not work for query parameters however, because the querystring function does not support Sets:

openapi-generator/modules/openapi-generator/src/main/resources/typescript-fetch/runtime.mustache

Lines 256 to 276 in 8d4c9e2

	export function querystring(params: HTTPQuery, prefix: string = ''): string {
	return Object.keys(params)
	.map((key) => {
	const fullKey = prefix + (prefix.length ? `[${key}]` : key);
	const value = params[key];
	if (value instanceof Array) {
	const multiValue = value.map(singleValue => encodeURIComponent(String(singleValue)))
	.join(`&${encodeURIComponent(fullKey)}=`);
	return `${encodeURIComponent(fullKey)}=${multiValue}`;
	}
	if (value instanceof Date) {
	return `${encodeURIComponent(fullKey)}=${encodeURIComponent(value.toISOString())}`;
	}
	if (value instanceof Object) {
	return querystring(value as HTTPQuery, fullKey);
	}
	return `${encodeURIComponent(fullKey)}=${encodeURIComponent(String(value))}`;
	})
	.filter(part => part.length > 0)
	.join('&');
	}

)

openapi-generator version

master