lb4 discover does not handle BLOB fields

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## Steps to reproduce
To reproduce this problem use lb4 discover in a MySQL table having a BLOB field. It will generate a model where BLOB is mapped to binary and does not start.

## Current Behavior

The lb4 discover blob fields as binary fields

## Expected Behavior

Blob fields should be discovered as buffer type.

## Link to reproduction sandbox

## Additional information

The created model property is like

```ts
@property({
type: 'Binary',
required: true,
length: 65535,
mysql: {columnName: 'photo', dataType: 'blob', dataLength: 65535, dataPrecision: null, dataScale: null, nullable: 'N'},
})
// Binary is not defined so compiler fails
// it should be Buffer
photo: Binary;
```
## Related Issues

No similar issues found.

_See [Reporting Issues](http://loopback.io/doc/en/contrib/Reporting-issues.html) for more tips on writing good issues_

Start by reproducing the issue with lb4 discover against a MySQL table containing a BLOB field, then inspect the generated TypeScript model shown in the report. Verify that BLOB is mapped to Buffer rather than the undefined Binary type and that the generated model compiles and starts successfully.

Scritto dal modello di indicizzazione a partire dal testo della issue.