GH-50581: [R] Use bundled simdjson by default

[Reranko05]

Rationale

The R build may pick up a system-installed simdjson when simdjson_SOURCE is not explicitly set. This causes build failures in environments where the system version is incompatible or unsuitable for the build.

What changes are included?

This change defaults simdjson_SOURCE to BUNDLED when it is not already set, ensuring the R build uses the bundled simdjson by default while still allowing users to override it explicitly.

This addresses the macOS CRAN release and ubuntu-r-only-r (AUTO deps) failures reported in GH-50581.

Related: #50581

• GitHub Issue: [R] R package build fails after simdjson introduction due to system simdjson pickup #50581

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[github-actions]

⚠️ GitHub issue #50581 has been automatically assigned in GitHub to PR creator.

[kou]

@github-actions crossbow submit -g r

[github-actions]

Revision: 9864597

Submitted crossbow builds: ursacomputing/crossbow @ actions-357652d8fe

Task	Status
r-binary-packages
r-recheck-most
test-r-alpine-linux-cran
test-r-arrow-backwards-compatibility
test-r-depsource-system
test-r-dev-duckdb
test-r-devdocs
test-r-extra-packages
test-r-fedora-clang
test-r-gcc-11
test-r-gcc-12
test-r-install-local
test-r-install-local-minsizerel
test-r-linux-as-cran
test-r-linux-rchk
test-r-linux-sanitizers
test-r-linux-valgrind
test-r-m1-san
test-r-macos-as-cran
test-r-offline-maximal
test-r-ubuntu-22.04
test-r-versions
test-r-wasm

[Reranko05]

@kou It looks like the remaining failures are related to the ongoing simdjson version discussion. If we go with requiring simdjson 4.0+ and falling back to the bundled version when the system package is too old, I think that should address this issue.