fix: dont use gulp streams for simple copying

[maribethb]

The basics

• I validated my changes

The details

Resolves

Fixes #2603

Proposed Changes

Uses fs methods for copying files instead of gulp streams

Reason for Changes

• gulp streams have overhead we don't need just to copy files without modification
• gulp streams set utf-8 encoding by default which was mangling our binary files (like pngs in blockly/media)

Test Coverage

Ran npm run test:ghpages to run the site locally and verified the trashcan issue is resolved and sounds now work in examples

Documentation

n/a

Additional Information

[mikeharv]

This looks like a solid fix!