docs(minifier): clarify assumptions for compressor (#8404)

Listed the assumptions that the compressor probably makes.

crates/oxc_minifier/README.md

@@ -18,6 +18,18 @@ The printer is also responsible for printing out the shortened variable names.
 The compressor is responsible for rewriting statements and expressions for minimal text output.
 [Terser](https://github.com/terser/terser) is a good place to start for learning the fundamentals.
 
+### Assumptions
+
+- [Properties of the global object defined in the ECMAScript spec](https://tc39.es/ecma262/multipage/global-object.html#sec-global-object) behaves the same as in the spec
+  - Examples of properties: `Infinity`, `parseInt`, `Object`, `Promise.resolve`
+  - Examples that breaks this assumption: `globalThis.Object = class MyObject {}`
+- [`document.all`](https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-IsHTMLDDA-internal-slot) is not used or behaves as a normal object
+  - Examples that breaks this assumption: `console.log(typeof document.all === 'undefined')`
+- TDZ violation does not happen
+  - Examples that breaks this assumption: `(() => { console.log(v); let v; })()`
+- `with` statement is not used
+  - Examples that breaks this assumption: `with (Math) { console.log(PI); }`
+
 ## Terser Tests
 
 The fixtures are copied from https://github.com/terser/terser/tree/v5.9.0/test/compress