(you don't have to strictly follow this form)

**Describe the bug**
When using `ORDER BY column_name COLLATE 'en'`, `COLLATE` is ignored if `column_name` is the primary key
 
**How to reproduce**
* version 21.1.2
* `CREATE TABLE` statements for all tables involved:
```
CREATE TABLE test.test_collation
(
    `v` String,
    `v2` String
)
ENGINE = MergeTree
ORDER BY v
SETTINGS index_granularity = 8192
```
* Sample data:
```
insert into test.test_collation values ('A', 'A')
insert into test.test_collation values ('B', 'B')
insert into test.test_collation values ('C', 'C')
insert into test.test_collation values ('a', 'a')
insert into test.test_collation values ('b', 'b')
insert into test.test_collation values ('c', 'c')
```
* Queries to run that lead to unexpected result
Primary key
```
SELECT *
FROM test.test_collation
ORDER BY v ASC COLLATE 'en'

Query id: fa84ae7a-abe7-4886-99cd-eba7ad5d5fc4

┌─v─┬─v2─┐
│ A │ A  │
│ B │ B  │
│ C │ C  │
│ a │ a  │
│ b │ b  │
│ c │ c  │
└───┴────┘
```
Separate column
```
SELECT *
FROM test.test_collation
ORDER BY v2 ASC COLLATE 'en'

Query id: 04401f85-3cb2-442c-8c89-e3328d1615cd

┌─v─┬─v2─┐
│ a │ a  │
│ A │ A  │
│ b │ b  │
│ B │ B  │
│ c │ c  │
│ C │ C  │
└───┴────┘
```

**Expected behavior**
Both of these queries to return the rows in the same order

{
            filter_info = filter_info_;
            filter_info->do_remove_column = true;
        }
        if (auto actions = query_analyzer.appendPrewhere(chain, !first_stage, additional_required_columns_after_prewhere))
        {
            prewhere_info = std::make_shared<PrewhereDAGInfo>(actions, query.prewhere()->getColumnName());
            if (allowEarlyConstantFolding(*prewhere_info->prewhere_actions, settings))
            {
                Block before_prewhere_sample = source_header;
                if (sanitizeBlock(before_prewhere_sample))
                {
                    ExpressionActions(
                        prewhere_info->prewhere_actions,
                        ExpressionActionsSettings::fromSettings(context->getSettingsRef())).execute(before_prewhere_sample);
                    auto & column_elem = before_prewhere_sample.getByName(query.prewhere()->getColumnName());
                    
                    if (column_elem.column)
                        prewhere_constant_filter_description = ConstantFilterDescription(*column_elem.column);
                }
            }
        }
        array_join = query_analyzer.appendArrayJoin(chain, before_array_join, only_types || !first_stage);
        if (query_analyzer.hasTableJoin())
        {
            query_analyzer.appendJoinLeftKeys(chain, only_types || !first_stage);
            before_join = chain.getLastActions();
            join = query_analyzer.appendJoin(chain);
            converting_join_columns = query_analyzer.analyzedJoin().leftConvertingActions();
            chain.addStep();