Sort tests by name when creating servo score report

[nicoburns]

This takes an object of the form:

{
    "test_name_3": { ... },
    "test_name_7": { ... },
    "test_name_1": { ... },
}

and turns it into:

{
    "test_name_1": { ... },
    "test_name_3": { ... },
    "test_name_7": { ... },
}

This makes it easier to compare the JavaScript and Rust implementations of the report generation, as we can apply the same sort on the Rust side and get a deterministic ordering.

Subtests are not sorted (original order is preserved) as they are listed in execution order which can be semantically important (execution order of whole tests is not important as they are independent (and also not present in the original report as tests are executed in parallel))