Improve error message when using mixed $ entries

[ericanderson]

https://github.com/palantir/osdk-ts/blob/main/packages/client/src/internal/conversions/modernToLegacyWhereClause.ts#L130-L137

Report was need to change:

$(Thing).where({
    age: {
        $gte: start;
        $lte: end;
    }
})

to

$(Thing).where({
  $and: [
    { age: { $gte: start } },
    { age: { $lte: end } }
  ]
}) 

Error message currently says:
Uncaught Error: Invariant failed: WhereClause Filter with multiple clauses isn't allowed