Eliminate `if (err instanceof Error)` pattern through helper function

[traeok]

Is your feature request related to a problem? Please describe.

When you have to handle an error in a TypeScript try/catch block, you need to verify that the parameter in the catch block is an Error before accessing any properties on it. If the value thrown is not instanceof Error we can just throw it as-is. We have this pattern in numerous places in the codebase.

Describe the solution you'd like

Implement a helper function to reduce duplicating this pattern.

Describe alternatives you've considered

Can continue adopting this pattern:

try {
    // some action that can throw error
} catch (err) {
    if (err instanceof Error) {
        // transform or doing something special
    }
    throw err;
}

But this pattern can be easily de-duplicated

Additional context

Came up while reviewing code in zowe/zowex

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[zFernand0]

GFI (good first issue)?

[Maanvi212006]

Hey @traeok @zFernand0 , I'd like to work on this!

Proposed Approach:

1. Create a new file packages/zowe-explorer-api/src/utils/ErrorUtils.ts with a handleError helper that wraps the instanceof Error check — calls a handler if it's a real Error, re-throws otherwise.
2. Export it from the package's index.ts so all packages can import it cleanly.
3. Do a codebase-wide find-and-replace of the existing pattern with calls to this helper.

I also noticed that a small errorToString(err: unknown): string utility could be useful alongside it — for cases where you just need to safely extract the error message without rethrowing. Happy to include that too if it sounds useful.

Let me know if the approach looks good or if there's a preferred location for shared utils!