Implement new client crate organization scheme

[jdisanti]

Implement the client crate organization RFC:

• Move crate::AppName, crate::Endpoint, crate::Credentials, and crate::Region into crate::config
• Move crate::PKG_VERSION into a new crate::meta module
• Move crate::operation::customize into crate::client
• Organize code generated types by operation
• Reorganize builders that aren't per-operation
• Only re-export aws_smithy_client::client::Builder for non-SDK clients (remove from SDK clients)
• Rename crate::types to crate::primitives
• Rename crate::model to crate::types
• Move crate::error into crate::types
• Move crate::ErrorExt into crate::error
• Re-export aws_smithy_types::error::display::DisplayErrorContext and aws_smithy_http::result::SdkError in crate::error
• Move crate::paginator into crate::operation
• Flatten crate::presigning
• Remove/hide operation ParseResponse implementations in crate::operation
• Hide or remove crate::lens and crate::http_body_checksum
• Update "Crate Organization" top-level section in generated crate docs
• Update the RFC status and checklist
• Add test the generated SDK crate that warns if any file is larger than 1MB