Generate CMake package files

[Chocobo1]

Downstream projects will now be able to find libchewing via CMake with the following:

find_package(Chewing REQUIRED)
target_link_libraries(someTarget PRIVATE Chewing::libchewing)

https://cmake.org/cmake/help/latest/guide/tutorial/Adding%20Export%20Configuration.html

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.43%. Comparing base (42d3e2e) to head (a0377c2).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #563 +/- ## ======================================= Coverage 88.43% 88.43% ======================================= Files 58 58 Lines 13537 13537 ======================================= Hits 11971 11971 Misses 1566 1566 ```

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