escape backslashes in JS string literal output

[digi-scrypt]

1. escapeDoubleQuote and escapeSingleQuote escape the closing quote but not the backslash, so a value ending in a backslash (or one before a quote) lands a \ right against the closing quote the printer adds and breaks out of the JS string literal.
2. these feed the renderComponent props object, slot names and the hoisted script src metadata, all built from attribute values in the source.

A quoted attribute is the trigger. <Component path='C:\dir\' /> currently emits {"path":"C:\dir\"} which node refuses to parse; a crafted trailing backslash terminates the string early and the following bytes are no longer inside it. Same story for src on a hoisted <script>.

Escaped the backslash first in both helpers. The one place escapeNewlines wraps the value I flipped the order so the \n it inserts isn't doubled. Added a snapshot covering a backslash attribute.

[changeset-bot]

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