Support building object_store and parquet on wasm32-unknown-unknown target

[jondo2010]

Which issue does this PR close?

Closes #180.

Rationale for this change

My goal is to get datafusion building and running on the wasm32-unknown-unknown target, and getting object_store and parquet are the first steps.

What changes are included in this PR?

This PR adds some conditional compilation in object_store (mostly around disabling local filesystem access), as well as shifting some dependencies to dev, and removing un-used features in deps (i.e. tokio).

Are there any user-facing changes?

None expected, this is purely a build-support change.

[tustvold]

FYI compiling with lz4 appears to fail

[tustvold]

Trying to compile object_store with non-default features returns an error about getrandom which appears related to https://docs.rs/getrandom/latest/getrandom/#webassembly-support

I'm not familiar enough with WASM to know if this is an issue or not?

[jondo2010]

Yep, wasm32-unknown-unknown is only going to support a limited set of features on parquet and object_store, in particular, the cloud storage features in object_store won't work, and some of the compression features on parquet won't work. I've documented everything in the respective READMEs now, and I also added a compile-time warning for object_store.

[ursabot]

Benchmark runs are scheduled for baseline = 4d5d10d and contender = f812d2c. f812d2c is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

[kylebarron]

and some of the compression features on parquet won't work

As a note on this, I've gotten zstd and lz4-flex to both compile to wasm, so it's possible to have better wasm parquet support if you're interested. For zstd I think it should work out of the box with arrow-rs IIRC (you may need to make sure you're building against the right clang, especially if on Mac, see https://github.com/kylebarron/parquet-wasm/pull/42/files). For lz4, we'd need to update arrow-rs to switch between lz4 and lz4-flex depending on whether building for wasm or not. See jorgecarleitao/parquet2#124 for the relevant code in parquet2. As of that, parquet2 builds to wasm32-unknown-unknown for all compressors. Ref also #180