[beta ] Revert "Ship gen_snapshot for linux-arm64 hosts targeting Android" (#186818)

This is a cherry-pick of this revert, which is needed because the change that was reverted caused a breakage in our release build.

Reverts: [Ship gen_snapshot for linux-arm64 hosts targeting Android](https://github.com/flutter/flutter/pull/182552)

Initiated by: @eyebrowsoffire

Reason for reverting: We do not have any bots capable of servicing this builder, and it is breaking our releases as well as `flutter precache --all`

Original PR Author: @dbebawy

Reviewed By: @reidbaker

The original PR description is provided below:

## Summary

Enable Android **profile** and **release** builds on ARM64 Linux hosts (AWS Graviton, GCP Tau T2A, self-hosted ARM64 runners, etc.), which currently fail because `gen_snapshot` is only shipped for `linux-x64` hosts.

Supersedes #182275 and #182276 — combined into a single atomic commit per reviewer feedback.

### Engine changes

- **`BUILD.gn`**: Make `gen_snapshot` and `analyze_snapshot` zip output names host-architecture-aware (`linux-arm64.zip` vs `linux-x64.zip`) using explicit `if (host_os == "linux" && host_cpu == "arm64")` branching, matching the existing pattern for mac/windows.
- **`linux_arm64_android_aot_engine.json`** (new): CI builder config following the secondary builder pattern (matching
`mac_android_aot_engine.json`). Only produces host-specific archives — shared artifacts (`artifacts.zip`, `symbols.zip`, embedding/abi jars) continue to be produced by the existing x64 Linux builder.
- **`.ci.yaml`**: New builder entry with `bringup: true`, `os=Linux`, `cpu=arm64`.

### Framework changes

- **`flutter_cache.dart`**: Convert `_linuxBinaryDirs` from a hardcoded `linux-x64` const list to a function parameterized by host architecture, using the existing `cache.getHostPlatformArchName()` pattern from `LinuxEngineArtifacts`.
- **`artifacts.dart`**: Clean up stale TODO comment — replace with accurate explanation of why `darwin-arm64` is remapped to `darwin-x64` (universal binary). No Linux remapping needed since Linux ships native binaries per host architecture.
- **Tests**: Add tests for both x64 and arm64 host artifact resolution in `cache_test.dart` and `artifacts_test.dart`, following the existing `LinuxEngineArtifacts` test pattern.

### Infrastructure notes

- The builder is set to `bringup: true` to allow stabilization before becoming a blocking builder.
- Requires ARM64 Linux machines in the LUCI swarming pool (`os=Linux` + `cpu=arm64`).
- 8 build configurations: {arm, arm64, x64, riscv64} × {profile, release}. This matches the x64 Linux builder's target coverage. The macOS equivalent has 6 builds (no riscv64).
- Uses RBE (`--rbe`) for remote compilation.

Fixes https://github.com/flutter/flutter/issues/75864 Fixes https://github.com/flutter/flutter/issues/168980

https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

## Test plan

### Verified by PR CI (x64 hosts)

### Requires ARM64 Linux hardware (post-bringup)

The new `linux_arm64_android_aot_engine` builder is `bringup: true` and does not run on PR checks. The `BUILD.gn` code path (`host_cpu == "arm64"`) is only exercised on ARM64 hosts. The following need to be validated once the builder runs on ARM64 infrastructure:

---------

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