Escape \0 followed by a number as a hex escape to avoid printing an octal

[weswigham]

Fixes #17226

[clydin]

This fix is breaking other use cases. For example, if there is a string literal node containing the text \0042, it will be emitted as \x00042 when it should not be altered (excepting the escape of the \) and definitely not include an extra 0.

[weswigham]

TBQH, we should be flagging string literal nodes containing octal escapes as errors - see #396, the reason being that they're ambiguous and behavior depends on the runtime (old or new). Specifically, under strict mode \0042 is just an error (which is why we never want to emit them).

[clydin]

I agree, but the error (and any normalization) should probably be at the parsing stage.
If an actual StringLiteral node's text is \0042 then the output of that node should be "\\0042" not "\\x00042" or "\\x0042". Just as if the node's text is \n; it's output would be (and currently is) "\\n". The printer should ideally be limited to generating syntactically correct output and not correcting for ambiguous behavior in input user code as such code should never (barring some hypothetical unsafe option) get that far into the full compilation pipeline.