build: Xcode based app bundle and code signing

[mentlerd]

Problem description

ImHex runs as full trust application on macOS with a non-compliant application bundle layout.

Implementation description

This PR introduces Xcode based application bundle generation, including code signing. Using Xcode ImHex can be built into a compliant application bundle with:

rm -r build
cmake --preset xcode -DCMAKE_PREFIX_PATH="$(brew --prefix llvm@17)"
cmake --build build/xcode
open build/xcode/Debug/imhex.app

Additionally, the resulting bundle can be adhoc code-signed and sandboxed by adding the CMake setting:

IMHEX_ENABLE_SANDBOXING_XCODE=YES

To make the application's bundle fully compliant fully compliant with the bundle spec the code had to be changed slightly:

Resources have moved from the Contents/MacOS directory to Contents/Resources, plugins have moved from Contents/MacOS/plugins to Contents/PlugIns as per the spec.

The application will still search for these resources in the original places too to preserve compatibility, and out-of-bundle build support.

Screenshots

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 1.51%. Comparing base (bdaf1e4) to head (eacd28f).

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Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1693   +/-   ##
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  Coverage    1.51%   1.51%           
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  Files         275     275           
  Lines       27008   27008           
  Branches    14474   14474           
======================================
  Hits          409     409           
  Misses      26341   26341           
  Partials      258     258           

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