Add bulk memory feature for wasm optimization.

[fnando]

What

Add wasm-opt's Feature::BulkMemory feature, so it can handle more contracts.

$ stellar contract optimize --wasm /Users/fnando/Downloads/02e9f32323236b7288dc2b3d4652db678dcd876301fb3852d9cfb7cfaf54e0d2.wasm --wasm-out ~/Downloads/optimized.wasm
⚠️ `stellar contract optimize` is deprecated and will be removed in future versions of the CLI. Use `stellar contract build --optimize` instead.
Reading: /Users/fnando/Downloads/02e9f32323236b7288dc2b3d4652db678dcd876301fb3852d9cfb7cfaf54e0d2.wasm (14026 bytes)
Optimized: /Users/fnando/Downloads/optimized.wasm (11453 bytes)

I optimized ALL contracts on the repo mentioned on #2290 successfully with this feature.

$ ls *.wasm | wc -l
    1799

$ ls optimized/*.wasm | wc -l
    1799

Why

Close #2290.

Known limitations

N/A