interp: handle bash >|, >>|, &>|, &>>|, <> redirects

[qiangli]

Summary

(*Runner).redir in interp/runner.go only threaded RdrIn, RdrOut, AppOut, RdrAll, and AppAll through its three dispatch switches. The remaining file-redirect operators that the parser already recognises — RdrClob (>|), AppClob (>>|), RdrAllClob (&>|), AppAllClob (&>>|), and RdrInOut (<>) — fell to the default: unhandled redirect op: %v branch and exited with an error, so any script using them failed even though plain >/>> worked.

This shows up most often in templates that wrap a user command in a fixed >| to force-overwrite a known temp file. With those failing, an embedded interpreter looks broken from the caller's perspective even when the user's command itself succeeded.

Approach

• Treat the four *Clob variants as identical to their plain counterparts. They only differ from >/>>/&>/&>> in that they bypass the noclobber shell option (set -C), and the interpreter does not enforce noclobber on file redirects today, so the runtime behaviour is the same.
• For <> (RdrInOut), open the target with O_RDWR|O_CREATE and bind it through stdinFile so reads work. Writes back through fd 0 are not propagated to the file because stdin is exposed as io.Reader internally — sufficient for the read-side use that accounts for nearly all real <> usage.

Test plan

• Four entries added to the existing redirect table in interp/interp_test.go covering >| (new file, overwrite-existing) and <> (read-existing, create-if-missing).
• go test -short ./interp/ ./syntax/ passes.
• Manual: the new redirect entries match bash 5.3 behaviour.