fix: Warning when export before enum - #18157

Preserve compatibility with cores that do not bind enums

When this plugin version is loaded by an older but supported @babel/core/@babel/traverse (the plugin's peer range is ^8.0.0), enums have no scope binding, so with optimizeConstEnums an input such as export const enum E { A } takes this branch and becomes Object.assign(E, ...) without ever declaring E, throwing during module evaluation. A missing binding must follow the declaration-creation path, and the paired traverse change must likewise remain compatible with older plugin versions.

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I am surprised that AI has also discovered this.

Clear bindings when inlining local const enums

With optimizeConstEnums, a non-exported const enum merged with a following namespace now leaves this newly registered binding behind when const-enum.ts removes the enum; the generic removal hook cannot clean it because getBindingIdentifiers has no TSEnumDeclaration entry. For a module containing const enum E { A } followed by namespace E { export const B = 1 }, transpileNamespace consequently sees hasOwnBinding("E") and omits its let E declaration, producing an IIFE that reads and assigns undeclared E and throws at runtime. Remove the enum binding before the inlining branch removes the declaration.

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While adding tests, I discovered that const enum cannot be merged with a namespace, but removing it is fine.

Register nested enums in their block scope

When an enum appears in a nested block and an enclosing function/program has a same-named binding, this new special case registers the enum in that enclosing scope because the collector routes non-BlockScoped declarations to the function/program scope. Consequently, valid shadowing such as let E; { enum E {} } throws Duplicate declaration "E" during scope crawling, even though the enum transform emits a block-local let; register enum declarations in their block parent (or classify them as block-scoped) instead.

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