GH-46816: [Docs] Fix links to Swift docs and source

[ianmcook]

Closes #46816

• GitHub Issue: [Docs] Fix links to Swift docs and source #46816

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit dcae309.

There were 119 benchmark results with an error:

• Commit Run on arm64-t4g-2xlarge-linux at 2025-06-15 11:29:15Z
  • tpch (R) with engine=arrow, format=parquet, language=R, memory_map=False, query_id=TPCH-07, scale_factor=1
  • tpch (R) with engine=arrow, format=native, language=R, memory_map=False, query_id=TPCH-09, scale_factor=1
• and 117 more (see the report linked below)

There were no benchmark performance regressions. 🎉

The full Conbench report has more details.