Implement partial include support

[davispuh]

Currently #include headers are dropped and not converted to D import statements.
This PR implements partial support so that include headers will be converted from:

#include <b.h>

to:

// FIXME: import b;

This allows to later process and fix them (for example with sed).
This is important when headers contain complicated inter-dependencies and without this information it's difficult to know which other files would need to be imported.

[Copilot]

Pull request overview

Adds partial #include preservation by converting include directives into emitted D imports (or // FIXME: import ...; placeholders) so downstream tooling can resolve dependencies later.

Changes:

• Parse #include directives in the preprocessor layer and expose them via IncludeDirective.
• Feed parsed include directives into IncludeHandler, and always emit placeholder // FIXME: import ...; lines for unhandled includes.
• Update unit tests’ expected translated output to include the newly emitted imports.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
dstep/translator/Preprocessor.d	Introduces IncludeDirective and parseInclude to recognize #include directives.
dstep/translator/Context.d	Collects parsed include directives and forwards them to IncludeHandler.
dstep/translator/IncludeHandler.d	Adjusts include ingestion and import emission; adds sys/ioctl mapping and emits // FIXME: import ...; for unknown includes.
dstep/translator/Options.d	Removes keepUntranslatable option (unhandled includes now always emitted).
tests/unit/issues/Issue85.d	Updates expected output to include core.stdc.stddef import.
tests/unit/issues/Issue8.d	Updates expected output to include core.stdc.stdint import.
tests/unit/issues/Issue199.d	Updates expected output to include core.stdc.stdint import.
tests/unit/UnitTests.d	Updates expected outputs to include stdc imports (incl. wchar_) when headers are present.
tests/unit/MacroTranslTests.d	Updates expected output to include core.stdc.stdint import.

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[jacob-carlborg]

Unfortunately there's no one-to-one mapping of header files and D modules, that's why handling of includes is incomplete. I'm not sure this is the right approach. I've been thinking about supporting generating bindings for a whole directory. Then it would be possible to look up where a declaration is located and add imports based on that instead of the includes.

There's also no new test case added.

[davispuh]

Unfortunately there's no one-to-one mapping of header files and D modules, that's why handling of includes is incomplete. I'm not sure this is the right approach. I've been thinking about supporting generating bindings for a whole directory. Then it would be possible to look up where a declaration is located and add imports based on that instead of the includes.

I looked into that and sadly it's not really possible to do it that way as show in #309. And even then how would you handle includes that are outside of specified dir so still would need something like this.
I think proper support can be added with dfix. That is after all .d files have been created, point dfix to that directory to automatically cleanup imports => remove unused ones and add missing ones by searching across files. Currently it doesn't have such feature but to me that seems like more realistic solution.

Anyway I rewrote this PR and added tests.
Note I included da7bdb9 commit from #297 here aswell.

[davispuh]

Found bug. Updated PR with fix and a test.