Decide on earliest platforms we support, and refuse to run on earlier platforms

[jfparadis]

Instead of supporting workarounds for bugs present on older platforms, maintain a narrow list of platforms, and perform sanity tests on load. See tc39/proposal-shadowrealm#175

• Procedurally limit supported versions through environment testing
• Emit diagnostic output for unsupported versions, both high and low. (We need better dependency diagnostic for too-old node versions #125)
• Document version support policy (Document minimum platform support for ses-shim #252)

[jfparadis]

Referencing comments by @erights in tc39/proposal-shadowrealm#175

The advisories: https://github.com/google/caja/wiki/SecurityAdvisories

For each of these, we should classify if they are relevant to modern Realms, Frozen Realms, or SES. Of the relevant ones, we should document whether there is anything there we should still worry about, and why or why not.

Especially interesting relevant advisory: https://github.com/google/caja/wiki/SecurityAdvisory20150313
Mostly, this advisory has to do with ancient browser bugs we no longer need to worry about. But we need to decide what the minimal versions are of all platforms that we do support, and ideally refuse to run on earlier platforms.

For the bugs of earlier platforms that we believe we no longer need to worry about on modern platforms, the old Caja/SES (usually in repairES5.js) has tests for those cases, to ensure they stay fixed. We need to make sure there are test262 tests for each of these, translating these old Caja/SES tests to test262 as needed.

Examples include both the advisory above and https://github.com/google/caja/wiki/SecurityAdvisory201308013

https://github.com/google/caja/wiki/SecurityAdvisory20130410 is an example of a vulnerability we have already fixed in the Realms shim, but only after independently rediscovering the issue.