[BUG] Deprecated function used in JavaScript and TypeScript generators

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

The current JavaScript and TypeScript generators use substr to get the date part (YYYY-MM-DD) from a full ISO-8601 date string, substr is deprecated and there is a substring function that is supported and that should be used instead.

Using deprecated functions might blocked by your build system.

Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr

openapi-generator version

Tested 6.6.0 and Master - Not a regression

Steps to reproduce

Generate any spec file containing a date field, the code generated is:

httpParams = httpParams.append(key, (value as Date).toISOString().substr(0, 10));

Related issues/PRs

Found no issue or PR mentioning this

Suggest a fix

Draft PR: https://github.com/OpenAPITools/openapi-generator/pull/15937

Start with the JavaScript and TypeScript generator output for a date field, using the shown TypeScript line as the reproduction target. Check the generator templates for uses of the deprecated function, compare the generated output with the suggested replacement, and run the relevant generator tests; the linked draft PR may already contain the work.