JS: Object.defineProperty "undefined namespaces" don't merge cross-file

[sandersn]

// @filename: 1.ts
Object.defineProperty(a.c, "prototype", { value: {} })
// @filename: 2.ts
const a = {}
a.c = function() { }

Expected behavior:
Behave the same as a.c.prototype = {} does today. (as seen in jsContainerMergeJsContainer)

Related Issues:
follow-on work discovered in #32944

[sandersn]

Turns out bindPotentiallyMissingNamespaces doesn't handle normal prototype properties either, presumably because a missing prototype property needs to be handled differently than a missing namespace. I'll close this since Object.defineProperty doesn't need to support what normal assignment doesn't.