Move cargo.toml to root

[prasannavl]

Summary

• Move cargo.toml to root
• Cleanup rebuild on head change in rust build scripts
• Move testdata into it's place
• Correct analyzer defaults for vscode
• Don't force SOLC_PATH requirement. It's prioritized, but will gracefully use path SOLC

Note: This is just another step in direction to make the build system more integrated.

Next step: Move rust to end of build process.

This PR makes it easier to run cargo directly if needed.

Eg: This allows

CARGO_TARGET_DIR=$(pwd)/build/target cargo build

or with in-built PROTOC and SOLC, pass them similarly or

export CARGO_TARGET_DIR=$(pwd)/build/target 
export SOLC_PATH=$(pwd)/build/depends/x86_64-pc-linux-gnu/bin/solc 
export PROTOC=$(pwd)/build/depends/x86_64-pc-linux-gnu/bin/protoc 

# Now can just run
cargo build

Implications

• Storage

  • Database reindex required
  • Database reindex optional
  • Database reindex not required
  • None

• Consensus

  • Network upgrade required
  • Includes backward compatible changes
  • Includes consensus workarounds
  • Includes consensus refactors
  • None

[prasannavl]

Pre-req pulled out into:

• Update and add example dev configs #2459
• Build scripts, testdata and SOLC housekeeping  #2460