Support import attributes

[nitsky]

Hi, the import attributes proposal is at stage 3 and has been implemented in V8 and other JavaScript engines. I would like to embed QuickJS in an application which requires import attributes support. Thank you!

[chqrlie]

This looks good. We would actually use this to read the reference file in microbench.js and the history file in repl.js. Loading tables as "csv" or files as "text" would be handy too.

[bellard]

done