fix(cli): escape single-quotes in dotenv key-values

[shamrt]

import-meta-env does not escape all interpolated values correctly; specifically, nested single quotes in a dotenv key-value; e.g.:

KEY1=['value3', 'value4']
KEY2="This has 'single quotes' inside"

— both of which are valid dotenv variables.

When running those values through the import-meta-env CLI util, we'd get the following (invalid JSON string):

<script>
  globalThis.import_meta_env = JSON.parse('{"KEY1":"['value3', 'value4']","KEY2":"This has 'single quotes' inside"}');
</script>

The unescaped single-quotes invalidate the JSON string ☹️

My team has worked around this locally — i.e. by treating invalid JavaScript as text, slicing off the JSON.stringify('') wrapper, and parsing it in a separate script so that the syntax is valid — but we wanted to raise this issue upstream and propose a fix.

There is an outstanding question about how we might want to handle single-quotes in the alternate RegExp conditions (via createScriptPlaceholderRegExp), so I'd be happy to extend this PR further to account for those situations.