Snapins: refresh the "Snapin File (exists)" selector after a save

[mastacontrola]

Problem

On the snapin edit page, uploading a new file on the General tab saves it to the storage node and sets it as the snapin's file. The page does not show that. The "Snapin File (exists)" selector keeps the old list and the old selection. The file input also keeps the upload, so a second Update sends the same file again.

Change

• After a successful save, the General tab clears the file input and re-reads the selector from a new getSnapinFileSelector sub. The sub selects the snapin's saved file.
• _snapinFileOptions() builds the options for both the page and the sub, so the two lists cannot drift.
• The selector row is always rendered, so it exists to fill after the first upload onto an empty node. fog.snapin.edit.js hides the row while it holds no files, as before.
• $.registerGeneralTab gains an optional onSuccess hook.
• FOG_BCACHE_VER 368 -> 369.

Access

The sub is get-prefixed, so Authorization::resolvePagePermission() maps it to view. That is the same rule getSnapinPrimaryStoragegroups uses. No permission change.

Testing

• Both phpstan passes are clean.
• Deployed to the 1.6 lab. Signed out, getSnapinFileSelector answers 401 JSON, the same as its sibling subs.
• Not yet run: the upload in a signed-in browser. On a throwaway snapin, upload a file with a new name, click Update, and confirm that the selector lists and selects the new file and that the file input is empty.

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