arrow

GH-39419: [C++][Parquet] Style: Using arrow::Buffer data_as api rather than reinterpret_cast (#39420)



### Rationale for this change

This patch using `{mutable}_data_as<T>()` api to replace `interpret_cast<{const} T*>`. It's just a style fixing.

### What changes are included in this PR?

Just api replacement for `::arrow::Buffer`

* `reinterpret_cast<T*>` -> `mutable_data_as<T>()`
* `reinterpret_cast<const T*>` -> `data_as<T>()`

Also, for `auto {variable_name} = reinterpret_cast<{mutable} T*>( ... )`, I changed it to:
1. `const auto*` for `data_as<T>()`.
2. `auto*` for `mutable_data_as<T>()`

This didn't change the syntax, but make it more readable.

### Are these changes tested?

No need

### Are there any user-facing changes?

no

* Closes: #39419 
* 

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