Fix plugins not showing up in Single Html mode

[anht3889]

Context

Fix #2194

Root cause:
We're using Set<String> jsFiles. The Set interface does not provide any ordering guarantees. We should make sure APP_JS at the top of other scripts.

Solution:
Use LinkedHashSet instead to guarantee the js scripts ordering.

Checklist

• Sign Allure CLA
• Provide unit tests

[CLAassistant]

All committers have signed the CLA.

[baev]

@anht3889 thanks!

fixed via #2220