Increase line coverage for Temporal

[anba]

Add tests to increase line coverage. Whenever possible, I've tried to copy the code style from other Temporal tests.

Steps performed:

• Compile SpiderMonkey with code coverage enabled.
• Run tests for a single class, e.g. built-ins/Temporal/ZonedDateTime/.
• Create grcov report to find missing coverage.
• Add tests for the missing coverage.
• Repeat step 2 with the next directory.

This PR doesn't address all missing coverage, for example Temporal.Duration still has some lines which aren't covered. I've also didn't yet run any tests under intl402/Temporal.