Switch DOMTimeStamp to EpochTimeStamp

[marcoscaceres]

Closes #103

The following tasks have been completed:

• [X] Modified Web platform tests - already tested

Implementation commitment:

• [x] WebKit (https://bugs.webkit.org/show_bug.cgi?id=231498)
• [ ] Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=1258483)
• [ ] Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=1735097)

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Preview | Diff

[reillyeon]

This seems totally reasonable but we should wait for LegacyTimeStamp to not be a broken link.

[marcoscaceres]

blocked on https://github.com/w3c/hr-time/pull/124/

[marcoscaceres]

Blocked on browser patches... but those should be quick to refactor.

[marcoscaceres]

Filed browser bugs... working on Gecko patch. Anyone willing to quickly do the others?