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GH-36970: [C++][Parquet] Minor style fix for parquet metadata (#36971)



### Rationale for this change

Minor style fix

### What changes are included in this PR?

1. Change `new` to `make_unique` or `make_shared`
2. Add a reserve for `column_order`

### Are these changes tested?

Not required.

### Are there any user-facing changes?

no

* Closes: #36970

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: Gang Wu <ustcwg@gmail.com>