ses's global contour bindings leak into Compartment lexical scope

SES safely executes third-party JavaScript 'strict' mode programs in compartments that have no excess authority in their global scope. Prior to version 1.12.0, web pages and web extensions using `ses` and the Compartment API to evaluate third-party code in an isolated execution environment that have also elsewhere used `const`, `let`, and `class` bindings in the top-level scope of a `<script>` tag will have inadvertently revealed these bindings in the lexical scope of third-party code. This issue has been patched in version 1.12.0. Workarounds for this issue involve either avoiding top-level `let`, `const`, or `class` bindings in `<script>` tags, or change these to `var` bindings to be reflected on `globalThis`.