rollupJoin measures are not considered when they are a SQL expression

**To Reproduce**
Using a measure like this in a rollupJoin does not work:
```
billmin: {
sql: `${CUBE.billsec}/60`,
type: `number`
},
```

**Expected behavior**
When the measure is an expression, but adheres to all requirements to be in a pre-aggregation query, like being addictive, it is expected that it will work like other measures that are not an expression.

**Version:**
0.27.42

**Additional context**
Seems that the code explicitly ignores expression measures from the computation. This is just one of the places that have that logic.

https://github.com/cube-js/cube.js/blob/d83717406363c7fcf755b7a7a23e2055c4929188/packages/cubejs-schema-compiler/src/adapter/BaseMeasure.js#L80

Also, the error message returned in that case, is really generic like below. Another improvement would be to have better error messages to clarify the reason it does not find the measures.
`Error: To join across data sources use rollupJoin with external pre-aggregations. Found data sources: voice, application`