Added [System.Flags] to enums that are flags.

[twindan]

Description

Some enums that are conceptually flags (e.g., SwsFlags) do no have [System.Flags] on the enum definition. This code adds that definition for the relevant classes.

What I do is look at the enum definition in ffmpeg when parsing. If it is of the form "1 << n", then I preserve the definition instead of collapsing the value (so the generated file say "VALUE = 1 << 3" instead of "VALUE = 8"). If all items in an enum are of the form 1 << n, then I treat it as a [System.Flags]. This seems to be how ffmpeg uses enumerated values.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code generation update
• Dependency update

Related Issues

#353

Testing

Ran the output

• I have tested my changes locally
• I have run dotnet build -c Release successfully
• I have run dotnet test -c Release successfully
• [N/A] I have tested with the example project if applicable

Checklist

• My code follows the project's code style
• [N/A] I have updated the documentation if needed
• [N/A] I have added tests for new functionality if applicable
• All existing tests pass
• I have checked that my changes don't introduce new warnings

Additional Notes

Output is the same except for enums that now have [System.Flags] appended. I have included the new generated files in this PR. Ran against ffmpeg commit 9047fa1b.

[Copilot]

Pull request overview

This PR updates the unsafe generator and regenerated enum outputs so that enums whose members are all expressed as single-bit shifts (1 << n) are emitted as C# flags enums ([Flags]) and preserve the shift-form instead of collapsing to numeric literals.

Changes:

• Updated enum processing to preserve = 1 << n expressions in generated enum member values (with appropriate numeric literal suffixes).
• Updated enum generation to emit using System; and add [Flags] to enums where every member value contains a left-shift.
• Regenerated Enums.g.cs outputs to reflect [Flags] and 1 << n formatting for the affected enums (e.g., SwsFlags, AVTimecodeFlag).

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated no comments.

File	Description
FFmpeg.AutoGen/generated/Enums.g.cs	Regenerated enums now include using System;, [Flags] on identified flags enums, and 1 << n member values.
FFmpeg.AutoGen.CppSharpUnsafeGenerator/Processing/EnumerationProcessor.cs	Preserves = 1 << n expressions during enum item value conversion via a generated regex.
FFmpeg.AutoGen.CppSharpUnsafeGenerator/Generation/EnumsGenerator.cs	Emits using System; and adds [Flags] when all enum items contain <<.
FFmpeg.AutoGen.Abstractions/generated/Enums.g.cs	Same regeneration as main package enums: using System;, [Flags], and 1 << n values where applicable.