Fixes the following shellcheck error:

    SC2068 (error): Double quote array expansions to avoid re-splitting elements.

https://www.shellcheck.net/wiki/SC2068

Fixes the following shellcheck error:

    SC2148 (error): Tips depend on target shell and yours is unknown. Add a shebang or a 'shell' directive.

https://www.shellcheck.net/wiki/SC2148

Fixes the following shellcheck errors:

    SC2145 (error): Argument mixes string and array. Use * or separate argument.
    SC2199 (error): Arrays implicitly concatenate in [[ ]]. Use a loop (or explicit * instead of @).

https://www.shellcheck.net/wiki/SC2145
https://www.shellcheck.net/wiki/SC2199

Also fixes a typo in SUPPORTED_INTERFACE_SWITCHER_MODES.

Fixes the following shellcheck error:

    SC2045 (error): Iterating over ls output is fragile. Use globs.

https://www.shellcheck.net/wiki/SC2045

Fixes the following shellcheck error:

    SC2081 (error): [ .. ] can't match globs. Use a case statement.

https://www.shellcheck.net/wiki/SC2081

Warns about shellcheck issues with severity `error`.