Write OpenFX plug-in for FileTransform

Issue #1117 requests OpenFX plug-ins for OCIO and Michael has PR #1371 in progress that is almost complete to implement a ColorSpaceTransform and DisplayViewTransform plug-in, which are the key ones. It would also be great to have a few more OpenFX plug-ins, for example for FileTransform. This would allow people to apply stand-alone LUTs in any of the formats OCIO supports, including the Academy/ASC Common LUT Format (CLF). The implementation should include an "invert" toggle button, similar to Michael's work.

It would also be great to have OpenFX plug-ins for LookTransform and NamedTransform, although these could also be in separate PRs.

OpenColorIO の既存の OpenFX プラグインのコンテキストを提供している issue #1117 と PR #1371 から始めます。invert トグルを含め、FileTransform プラグインを ColorSpaceTransform および DisplayViewTransform の作業とどのように並行して組み込むべきかを判断します。FileTransform OpenFX プラグインが CLF を含むサポート対象のスタンドアロン LUT 形式を適用できれば完了です。LookTransform と NamedTransform は別のフォローアップ範囲です。

索引モデルが issue の本文から書いたものです。