[legacy-framework] Fix issue with using non-page files inside pages folders

[ryardley]

Closes: blitz-js/legacy-framework#470

What are the changes and their implications?

• Only copy typescript/javascript files to the pages folder - leave other extensions where they are.
• Allow imports to be relative transformed when import does not have an import specifier.

Checklist

• Tests added for changes
• PR submitted to blitzjs.com for any user facing changes

[ryardley]

Just realised we are not doing path transformation when imports don't use the from syntax with an import specifier. So adding it to this PR.

[flybayer]

Awesome, thanks!