Based on a feedback from
#128456 (comment)

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Renames compression option APIs that exposed `WindowLog` so the public
surface consistently uses `WindowLog2` for base-2 log values, including
the matching Zstandard decompression property `MaxWindowLog2`.

- **API surface**
  - `BrotliCompressionOptions.WindowLog` → `WindowLog2`
  - `ZLibCompressionOptions.WindowLog` → `WindowLog2`
  - `ZstandardCompressionOptions.WindowLog` → `WindowLog2`
  - `ZstandardDecompressionOptions.MaxWindowLog` → `MaxWindowLog2`
  - Aligns related public members to the same naming:
- zlib/zstd `DefaultWindowLog*`, `MinWindowLog*`, `MaxWindowLog*` →
`*WindowLog2`
- encoder / decoder parameter names `windowLog` / `maxWindowLog` →
`windowLog2` / `maxWindowLog2`

- **Implementation updates**
- Updates all in-repo call sites, option consumers, constructors, ref
files, platform stubs, XML docs, and error text.
- Ensures thrown `ArgumentOutOfRangeException.ParamName` values match
the renamed public parameters.

- **Compatibility**
- This is an intentional public API rename; no compatibility alias/shim
is added.

- **Example**
  ```csharp
  var options = new ZstandardCompressionOptions
  {
      Quality = 3,
      WindowLog2 = 20
  };

  var decompressionOptions = new ZstandardDecompressionOptions
  {
      MaxWindowLog2 = 20
  };
  ```

- **Validation**
  - Rebuilt `System.IO.Compression` and `System.IO.Compression.Brotli`
  - Ran targeted test projects:
    - `System.IO.Compression.Tests`
    - `System.IO.Compression.Brotli.Tests`

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>