Use /proc/self instead of /proc/<pid> in getOpenedPath

[ptarjan]

When running in a PID namespace (common in containers), watchman fails
with "need /proc to be mounted!" because it accesses /proc//fd/X
using the namespace PID, but /proc may be mounted from the host with
different PID numbering.

The fix is to use /proc/self/fd/X instead of /proc/<getpid()>/fd/X
when resolving file descriptor paths. The /proc/self symlink is always
resolved by the kernel to the current process's /proc entry, regardless
of PID namespace boundaries.

This issue manifests when:

• Process is in a PID namespace (e.g., Docker container)
• /proc is mounted from host or a different namespace
• watchman tries to resolve paths via /proc//fd

Error seen:
getOpenedPath: need /proc to be mounted!: Function not implemented

Affected platforms: Linux containers with PID namespace isolation

[meta-codesync]

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[facebook-github-bot]

@ptarjan has updated the pull request. You must reimport the pull request before landing.

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@ptarjan has updated the pull request. You must reimport the pull request before landing.

[ptarjan]

@ptarjan has updated the pull request. You must reimport the pull request before landing.

I'm doing this to re-run the flaky test

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@ptarjan has updated the pull request. You must reimport the pull request before landing.

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@ptarjan has updated the pull request. You must reimport the pull request before landing.

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[ptarjan]

I'm giving up on CI. It is failing on main. The code compiles and works on my machine and I tested in my fleet and it works great.