[CMake] Enable automatic cmake config discovery

[Ubospica]

Relocate CMake config files from cmake/ to share/cmake/tvm_ffi/ to match
CMake's standard search pattern <prefix>/<name>*/share/cmake/<name>*/.

This enables find_package(tvm_ffi CONFIG REQUIRED) to work automatically
without manually setting tvm_ffi_ROOT.

When find_package(Python) is called, CMake adds sys.prefix to search paths,
allowing it to discover tvm-ffi's config files in the standard location.

This also aligns with pybind's behavior. See also https://github.com/pybind/pybind11/blob/a2c59711b20707d64b7ad61d488e002611369780/.github/CONTRIBUTING.md#L325 and https://github.com/pybind/pybind11/blob/a2c59711b20707d64b7ad61d488e002611369780/pybind11/commands.py#L22.

Changes:

• CMakeLists.txt: Install config to share/cmake/tvm_ffi/
• libinfo.py: Update find_cmake_path() to check standard path first
• examples: Simplify CMakeLists.txt to use direct find_package()

This PR also avoids rebuilding in editable installation mode, and adds a cd command in the readme of examples to ensure user is in the correct directory.

[gemini-code-assist]

Summary of Changes

Hello @Ubospica, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the usability and integration of tvm_ffi with CMake-based projects. By relocating CMake configuration files to a standard share/cmake directory, tvm_ffi can now be automatically discovered by find_package, eliminating the need for manual path configuration. This change simplifies project setups, particularly for examples, and optimizes the editable installation process by preventing redundant builds.

Highlights

• CMake Config Relocation: CMake configuration files for tvm_ffi are now installed to share/cmake/tvm_ffi/ to align with standard CMake search patterns, improving discoverability.
• Automatic Discovery: find_package(tvm_ffi CONFIG REQUIRED) now automatically discovers the tvm_ffi CMake configuration without needing to manually set tvm_ffi_ROOT.
• Simplified Examples: Example CMakeLists.txt files have been simplified by removing manual calls to tvm_ffi.config for CMake path discovery, making them cleaner and easier to use.
• Editable Install Optimization: The build system is configured to avoid unnecessary rebuilding when performing an editable installation, streamlining the development workflow.
• Improved Example Readme: README.md files in examples now include cd commands to ensure users are in the correct directory before running installation or build commands, preventing common user errors.

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[gemini-code-assist]

Code Review

This pull request makes a valuable improvement by relocating the CMake configuration files to a standard directory, which enables automatic discovery by CMake's find_package. This simplifies the integration for downstream projects, as demonstrated by the cleanup in the example files. The addition of editable.rebuild = false is also a nice touch for improving the developer workflow during editable installs.

My review found one issue in python/tvm_ffi/libinfo.py where the path to the new CMake directory is constructed incorrectly for standard installations. I've left a specific comment with a suggested fix. Otherwise, the changes are well-implemented and align with the stated goals.

[junrushao]

Nice work!! I was about to ask :)

[tqchen]

note that this unfortunately does not work for cmake that is outside of scikit build part, so we still need to keep the cmake path for max compact