#3230 fix: keep npm and npx shims working for symlinked tool binaries

Summary

npm and npx were not found after installing nodejs/node through tools. The shims in the tools bin dir were dangling symlinks.

Changes

• Skip the hardlink in createShimFile when the target is itself a symlink, and point the shim at the target's absolute path instead. link(2) does not follow symlinks on Linux, so the old code copied node's relative npm -> ../lib/node_modules/npm/bin/npm-cli.js link into the bin dir, where it dangled.
• Dangling shims from earlier installs are replaced on the next install.
• Add a test for a symlinked target that also replaces a dangling shim.

Related Issues

Closes #3229

Checklist

• Code follows the project style guidelines
• Self-review of the code has been performed
• Tests have been added or updated as needed
• Documentation has been updated as needed
• Changes have been tested locally

Tested with go test ./internal/tools/....

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Summary by cubic

Fixes npm and npx not being found after installing nodejs/node through tools, caused by dangling shims in the bin dir.

Hard-linking a symlinked target copied the relative link (e.g. npm -> ../lib/node_modules/npm/bin/npm-cli.js) into the bin dir, where it dangled. Shims now point at the target's absolute path when the target is a symlink, and dangling shims from earlier installs are replaced on the next install. Added a test covering both behaviors. Closes #3229.

Summary by CodeRabbit

• Bug Fixes
  • Fixed command shims for symlinked executable targets. When an executable is reached through a symlink, the shim now uses an appropriate fallback instead of creating a hard link to the symlink itself. This helps prevent dangling shims and ensures the resulting command remains executable and points to the intended target.