Support injecting scriptlets in one shared scope

[chrmod]

Each scriptlet func inlines its own safeSelf(), so stacked hooks compound (2^n). #63 shares 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 adds what the extension needs for that:

• functions: every function once; each scriptlet gets fn and dependencies
• compose(calls, scriptletGlobals): one code string per injection, for registered scripts and chrome.userScripts.execute
• run(scriptletGlobals, calls): one self-contained function for chrome.scripting.executeScript

func stays for now. Once ghostery-extension uses the new exports it is unused and can go together with the Symbol.for cache.