Clarify the difference between `--yul`, `--assemble` and `--strict-assembly` in the CLI help

On the CLI we have 3 options for compiling Yul, and they're different but their descriptions do not explain how. To users `--yul` seems like the natural choice and the result is confusion (e.g. [How to compile IR into bin?](https://forum.soliditylang.org/t/how-to-compile-ir-into-bin/1146)).

The options will likely change after #7830 but we should clarify the CLI help even before then.

### Current descriptions
```
--assemble Switch to assembly mode, ignoring all options except
--machine, --yul-dialect, --optimize and
--yul-optimizations and assumes input is assembly.
--yul Switch to Yul mode, ignoring all options except
--machine, --yul-dialect, --optimize and
--yul-optimizations and assumes input is Yul.
--strict-assembly Switch to strict assembly mode, ignoring all options
except --machine, --yul-dialect, --optimize and
--yul-optimizations and assumes input is strict
assembly.
```

Start by locating the CLI help definitions for --yul, --assemble, and --strict-assembly, then compare their documented behavior with the concerns in #7830. Clarify the descriptions so users can distinguish the three compilation modes, and verify the resulting CLI help output.

Written by the indexing model from the issue text.