crate_universe: use local paths for vendored crate aliases

[goutamadwant]

Fix local crates_vendor alias generation for path dependencies in local
vendor mode.

When a crate is patched to a local path, generated hub aliases and entries
from crate_deps() now target the in-repository Bazel package instead of an
external repository label. Local labels are constructed through a shared
validated path so malformed or escaping paths return a rendering error.

The local-patching integration fixture now exercises both the generated hub
alias and the crate_deps() lookup for a patched getrandom dependency.

Fixes #3732

Tests:

• bazel test //crate_universe:unit_test --nocache_test_results
• bazel build //crate_universe:unit_test --config=rustfmt --config=clippy
• bazel test //local_patching:test //local_patching:crate_deps_test

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