Build scripts: Name client variants by their build system for clarity

[jul-sh]

TL;DR

cpp -> bazel
rust -> cargo
nodejs -> npm

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Addresses @daviddrysdale's earlier comment: #1169 (comment)

This renames the issue of the somewhat confusing cpp variant.

This makes sense, since bazel is the build system the scripts will use for this variant. And other non cpp clients (Go) that use bazel shouldn't use the cpp flag.

Similarly this renames rust to cargo, and nodejs to npm, so we always refer to the build system.

This is quite similar to the naming used in the rust runner.

oak/runner/src/main.rs

Line 295 in 19ff6bb

enum Target {

Imho it might be worth to think about doing the same for the server/application variants.

Checklist

• Pull request affects core Oak functionality (e.g. runtime, SDK, ABI)
  • I have written tests that cover the code changes.
  • I have checked that these tests are run by
    Cloudbuild
  • I have updated documentation accordingly.
  • I have raised an issue to
    cover any TODOs and/or unfinished work.
• Pull request includes prototype/experimental work that is under
  construction.

[jul-sh]

This also means we now explicitly check for the presence of a BUILD file.

[github-actions]

Reproducibility Index:

c7e447de8c9dc9456f7a8ba83959474a39970eb4967998fe0b908f92f0a4d89b  ./examples/target/wasm32-unknown-unknown/release/abitest_0_frontend.wasm
7197a5c68eaf0d2d5ae226ea1cb8dbf1a5a3b499c8a205e5d7a0537faa7dcd1f  ./examples/target/wasm32-unknown-unknown/release/abitest_1_backend.wasm
20c9b09fd04da0a06a69f6343eaf0f3afd7bbf97304e3a08464e13f185feb969  ./examples/target/wasm32-unknown-unknown/release/aggregator.wasm
0bdbe9ec58af36a1c50311a598bdc0bb09327ba4ea9aa4abd0d5c4ce6426bf02  ./examples/target/wasm32-unknown-unknown/release/chat.wasm
c0f0cfc1d370b0adfe7907d79f8afa0548f2f77dc7ef8aa5a17be3405f30cd76  ./examples/target/wasm32-unknown-unknown/release/hello_world.wasm
97f2f2eff51281290bd836ed86cffc8999718659431d0f5f8468d1afcaa24cdf  ./examples/target/wasm32-unknown-unknown/release/machine_learning.wasm
a3e0afddba46224ca81f1a43a163e9f0c47fe106bd5f670ead206610939db449  ./examples/target/wasm32-unknown-unknown/release/private_set_intersection.wasm
2ed84ec712fbfc733e204a6ed1af7651f7b9b1bc241878adb17c6ea301a233d1  ./examples/target/wasm32-unknown-unknown/release/running_average.wasm
f42dae0e0c31c6dea9766ee2441327d95de2242990d024d68e99b431a414c562  ./examples/target/wasm32-unknown-unknown/release/translator.wasm
f2f4a2ced4d1af2c4fde34361742d3bceae636c6bfcc468af92e9b4be5427ad7  ./examples/target/wasm32-unknown-unknown/release/trusted_information_retrieval.wasm
75bb864495cbb7278f8fdc8d25f050323d9dc281f9528f3f789835def25e4e7f  ./oak/server/target/x86_64-unknown-linux-musl/release/oak_loader

Reproducibility Index diff: