xtask: Use a single Swift module when building the bindings.

[pixlwave]

Xcode 26.4 didn't like the modulemap we were generating. It used to look like so:

module matrix_sdkFFI {
    header "matrix_sdkFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

module matrix_sdk_cryptoFFI {
    header "matrix_sdk_cryptoFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

module matrix_sdk_ffiFFI {
    header "matrix_sdk_ffiFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

module matrix_sdk_commonFFI {
    header "matrix_sdk_commonFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

module matrix_sdk_baseFFI {
    header "matrix_sdk_baseFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

module matrix_sdk_uiFFI {
    header "matrix_sdk_uiFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

I think the main issue was that this defines modules that don't match the MatrixSDKFFI name defined by the Package.swift files (SDK / Components). It seems this is now not allowed.

This PR updates the consolidation to a single module containing all of the headers:

module MatrixSDKFFI {
    header "matrix_sdkFFI.h"
    header "matrix_sdk_cryptoFFI.h"
    header "matrix_sdk_ffiFFI.h"
    header "matrix_sdk_commonFFI.h"
    header "matrix_sdk_baseFFI.h"
    header "matrix_sdk_uiFFI.h"
    export *
    use "Darwin"
    use "_Builtin_stdbool"
    use "_Builtin_stdint"
}

To make this work we then need to make sure all the of .swift files import MatrixSDKFFI now instead of whatever their corresponding UniFFI module name was.

Fixes matrix-org/matrix-rust-components-swift#32
Fixes element-hq/element-x-ios#5321

• I've documented the public API Changes in the appropriate CHANGELOG.md files.
• This PR was made with the help of AI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.88%. Comparing base (c04a97f) to head (44db10d).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6388      +/-   ##
==========================================
+ Coverage   89.86%   89.88%   +0.02%     
==========================================
  Files         377      377              
  Lines      103167   103167              
  Branches   103167   103167              
==========================================
+ Hits        92710    92734      +24     
+ Misses       6893     6883      -10     
+ Partials     3564     3550      -14     

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[codspeed]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing doug/xcode-26.4 (44db10d) with main (c04a97f)}

[Hywan]

Looks good to me! Thank you for fixing the problem.

[Hywan]

Nice trick to insert a vec in a vec.