fix(vite): decode dots in prebundled subpath specifiers - #11466

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

Vite's flattenId encodes / as _ and . as __. viteDepsPathToBareSpecifier (and the shared-alias lookup next to it) decoded a vendored package's subpath by turning every _ into /, so dots came back as //. For example, pkg_lib_file__js became pkg/lib/file//js, and the request 404'd.

What is the new behavior?

One decodeFlattenedSubpath helper decodes __ to . first, then _ to /, and both decode sites use it.

Tests: packages/vite/hmr/server/websocket-module-specifiers.prebundle.spec.ts (3) covers a dotted subpath, an extensionless subpath, a scoped package, and the package's own prebundle.