Allow `read` builtin to take input from non-tty `stdin`

Created by: huntergoldstein

Reproduction: Attempt to have read take input from anything except a terminal, for example:

$ echo foo | read bar

Expected behavior:

$ echo foo | read bar
$ echo $bar
foo

Actual behavior:

$ echo foo | read bar
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Custom(Custom { kind: Other, error: StringError("Unable to get Termios attribute.") }) }', /checkout/src/libcore/result.rs:860:4
$ echo $bar
<no output>

Build information:

• git rev-parse HEAD: 2c62ffb8

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The solution to this is to have the read builtin determine if its stdin is a tty or not; if so, it will use the nice liner prompt, otherwise it will read the next line from stdin.