Support injecting scriptlets in one shared scope

[chrmod]

Each scriptlet func inlined its own safeSelf(), so stacked hooks compounded (2^n). #63 shared the cache through a Symbol.for property on globalThis, which pages can enumerate and use to reach the unhooked natives.

uBO avoids this by running all scriptlets of a frame in one scope with each dependency declared once. This replaces the per-scriptlet func wrappers and the global with:

• an index of scriptlets with aliases, world, requiresTrust and fn
• run(scriptletGlobals, calls): one function that declares every uBO function once and calls the requested scriptlets; the extension passes it to chrome.scripting.executeScript and serializes it for registered scripts

Bundle goes from 2.2 MB to 0.24 MB.