rust_analyzer: fix target exclusions in gen_rust_project

[ptsteadman]

gen_rust_project did not support target exclusion patterns (e.g. -//util/process_wrapper/...). Two bugs:

1. lib.rs: bazel build received exclusion patterns before the end-of-options marker --, so Bazel rejected them as unknown flags.
2. aquery.rs: the deps() expression was constructed by joining all targets with + (e.g. deps(//util/...+-//util/process_wrapper/...)), which is invalid aquery syntax. Exclusions need to use - instead.

Before (main), fails at bazel build:

$ bazel run @rules_rust//tools/rust_analyzer:gen_rust_project -- -- //util/... -//util/process_wrapper/...
ERROR: Invalid options syntax: -//util/process_wrapper/...
Note: Negative target patterns can only appear after the end of options marker ('--').
Error: bazel build failed: (exit status: 2)

After (this branch), full round-trip succeeds:

$ bazel run @rules_rust//tools/rust_analyzer:gen_rust_project -- -- //util/... -//util/process_wrapper/...
INFO: running bazel build...
INFO: bazel build finished
INFO: running bazel aquery...
INFO: bazel aquery finished; parsing spec files...
# rust-project.json written with action_args, collect_coverage, label, workspace_status
# (process_wrapper excluded as expected)

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