zFTP: Spool files are not listed properly for active jobs

[traeok]

Describe the bug

Related: zowe/zowe-cli-ftp-plugin#156

Spool files are not listed properly for active jobs using a zFTP profile. This applies to both v2 and v3.
This is a limitation in zos-node-accessor: https://github.com/IBM/zos-node-accessor/blob/60cdfd26eea001686d50a92128f12a6fff0f91ca/lib/zosAccessor.js#L867-L868

To Reproduce

• Try to expand a job that's active under a zFTP profile
• Notice that there is only one spool file listed, named [(0)], and it has no information
• Opening said file results in an editor tab named 0 to appear with no contents

Expected behavior

We should either:

• show a placeholder node to say that FTP profiles do not support listing spool files for active jobs
• not show any spool files

I prefer the first option because it provides context for the failure when listing spool files.

Screenshots

Desktop (please complete the following information):

• OS: Windows 10
• Zowe Explorer Version: v2.15.2

[github-actions]

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We will investigate the bug and evaluate its impact on the product.
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[traeok]

@JillieBeanSim suggested that we should catch any errors from the extender and then handle those errors accordingly in Zowe Explorer. In hindsight, I prefer this option over the above solutions mentioned, because it is consistent with our expectations for extenders to handle errors where applicable.

[JillieBeanSim]

closing with merge of linked PR