Distinguish between Wasm runtime and execution environment

The ecosystem could benefit from establishing terminology to explain the difference between a Wasm runtime and a project that uses a Wasm runtime under the hood. For example, both Spin and WasmCloud execute Wasm using the Wasmtime runtime. What do we call those projects? "Execution environment" is one option.

No file, test, or entry point is identified. Start by reviewing the distinction in this issue and the examples of Spin, WasmCloud, and Wasmtime; done means proposing terminology that clearly separates a Wasm runtime from projects that use one.

Written by the indexing model from the issue text.