Fix nested var redeclaration crash · Pull Request !7341 · OpenHarmony/arkcompiler_ets_frontend

1. Fix nested var redeclaration crash
---
### Issue:
[[Bug]: nested var declaration crash](https://gitee.com/openharmony/arkcompiler_ets_frontend/issues/ICOB1Z)

### Reason:
FindLocal only searches the current scope, so inner `var x` couldn’t see an existing outer `let x` or function‐scoped `var x`, causing AddBinding to return nullptr and trigger an assertion failure.

### Description:
In `Scope::AddDecl`, when declaration is var-declaration, add ```Find(decl->Name(), ResolveBindingOptions::BINDINGS).variable``` to perform a full scope‐chain lookup. This ensures redeclarations throw an error instead of crashing.

### Tests:
ninja tests passed
tests/tests-u-runner/runner.sh --ets-cts --show-progress --build-dir x64.release --processes=all passed
tests/tests-u-runner/runner.sh --ets-func-tests --show-progress --build-dir x64.release --processes=all passed
tests/tests-u-runner/runner.sh --astchecker --show-progress --build-dir x64.release --processes=all passed
tests/tests-u-runner/runner.sh --ets-runtime --show-progress --build-dir x64.release --processes=all passed
tests/tests-u-runner/runner.sh --parser --no-js --show-progress --build-dir x64.release --processes=all passed

Change-Id: I04fb10c850fc1dfc4f3c20b57daa49d6f8a44a02

类型	指派人员	状态
审查	@egavrin 由 CODEOWNERS 文件第 18 行指派为审查者	进行中 (0/1人)
审查	godmiaozi zhuoli72 gavin1012_hw 徐城 Ilya Trubachev Urakov Alexandr Chernykh Sergey Vsevolod Pukhov	进行中 (0/1人)
测试	openharmony_ci 已测试通过	已完成 (1/1人)

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