[ELF] Adjust --compress-sections to support compression level

zstd excels at scaling from low-ratio-very-fast to
high-ratio-pretty-slow. Some users prioritize speed and prefer disk read
speed, while others focus on achieving the highest compression ratio
possible, similar to traditional high-ratio codecs like LZMA.

Add an optional `level` to `--compress-sections` (#84855) to cater to
these diverse needs. While we initially aimed for a one-size-fits-all
approach, this no longer seems to work.
(https://richg42.blogspot.com/2015/11/the-lossless-decompression-pareto.html)

When --compress-debug-sections is used together, make
--compress-sections take precedence since --compress-sections is usually
more specific.

Remove the level distinction between -O/-O1 and -O2 for
--compress-debug-sections=zlib for a more consistent user experience.

Pull Request: https://github.com/llvm/llvm-project/pull/90567