Yul: add comments on function dispatcher.

The yul code is sometimes hard to read.
When optimized, the main dispatch looks like:
```
let _2 := 0
switch shr(224, calldataload(_2))
case 0x1a212539 {
if callvalue() { revert(_2, _2) }
...
```
It is very nice that the public functions are inlined. but it makes the code very hard to read.
when the code is unoptimized, the code is slightly more readable:

```
switch shr(224, calldataload(0))
case 0x1a212539 { external_fun_xxx() }
case 0x1e13bcd2 { external_fun_yyy() }
```

### Suggestion:
add a comment near the "case xxxx", with the external method name (or its full signature)

Start by locating the Yul function-dispatcher generation path and compare the optimized and unoptimized output shown in the issue. Trace how selector cases are emitted; done means optimized dispatch output includes the external method name or full signature while preserving dispatch behavior.

Written by the indexing model from the issue text.