vm: lexical declaration no longer throws SyntaxError over a global function declaration in vm context (regression in v26.6.0)

### Version v26.6.0 ### Platform ```text Darwin 24.6.0 Darwin Kernel Version 24.6.0: xnu-11417.140.69.705.2~1/RELEASE_ARM64_T6041 arm64 (macOS, Apple Silicon) ``` ### Subsystem _No response_ ### What steps will reproduce the bug? A `let` declaration that collides with a name introduced by a **function declaration** in a previous script in the same vm context is no longer rejected with a `SyntaxError`: ```js const vm = require('vm'); const context = vm.createContext({}); // A function declaration in global (script) code appends its name to the // global environment record's [[VarNames]] (CreateGlobalFunctionBinding). vm.runInContext('function foo() { return 42; }', context); // Per ECMA-262 GlobalDeclarationInstantiation, HasVarDeclaration('foo') is // then true, so this lexical declaration must throw. try { vm.runInContext('let foo;', context); console.log('NO ERROR (let foo; was accepted)'); } catch (e) { console.log('THREW:', e.constructor.name, '-', e.message); } // Fallout: the accepted `let` shadows the still-present function. console.log('typeof foo ->', vm.runInContext('typeof foo', context)); console.log('this.foo() ->', vm.runInContext('this.foo()', context)); ``` ### How often does it reproduce? Is there a required condition? 100% reproducible. ### What is the expected behavior? Why is that the expected behavior? `let foo;` should throw a `SyntaxError`. `CreateGlobalFunctionBinding` appends the name to the global environment record's `[[VarNames]]`, so on the next script `HasVarDeclaration('foo')` is true and GlobalDeclarationInstantiation must throw. v26.5.1 behaves correctly: ``` THREW: SyntaxError - Identifier 'foo' has already been declared typeof foo -> function this.foo() -> 42 ``` ### What do you see instead? On v26.6.0 the declaration is silently accepted, and the new lexical binding shadows the function — calling it by name now fails while it is still reachable as a property of the global object: ``` NO ERROR (let foo; was accepted) typeof f…