Automatically add a results table for CI runs on pull requests

[ptomato]

I've noticed several times that the meaning of the CI results is confusing for contributors:

This looks like it is saying "all engines passed these tests." What it really means is "all engines installed correctly and executed these tests without crashing, regardless of pass or fail."

Likewise, this looks like it means "ChakraCore failed these tests, all other engines passed." What it really means is "ChakraCore failed to install."

I think we could reduce this confusion by automatically posting individual test results to a table in a PR comment. For example, the table for #4052 might look like this:

Test name	engine262	ESMeta	JSC	SpiderMonkey	V8	V8 --harmony	XS
language/expressions/assignment/target-member-computed-reference.js	❌	✅	❌	✅	❌	✅	❌
language/expressions/assignment/target-super-computed-reference.js	✅	❌	✅	❌	✅	❌	✅

(pass/fail status is entirely made up and not a comment on any engine)

ci_test.sh already runs only the added and modified tests on each engine, and just discards the results; we could easily consume those results to build the table.

[ljharb]

That would be great. What would be even better if the table only included results that were different from the last successful run on main.