CMake: Canonicalize rapidjson include path in RapidJSONConfig.cmake.

[bastianbeischer]

Having the path without relative components allows other projects to add the RadidJSON_INCLUDE_DIRS as a system include directory, without causing problems in the build.

[tencent-adm]

All committers have signed the CLA.

[bastianbeischer]

See discussion in:

https://github.com/MaskRay/ccls/pull/383

(specifically the last comment)

[coveralls]

Coverage increased (+0.001%) to 99.922% when pulling c9b57bd5f7cfd0e3ad1e256dbab4a4dd28e8ad33 on bastianbeischer:cmake into 01950eb7acec78818d68b762efc869bba2420d82 on Tencent:master.

[coveralls]

Coverage increased (+0.001%) to 99.922% when pulling c9b57bd5f7cfd0e3ad1e256dbab4a4dd28e8ad33 on bastianbeischer:cmake into 01950eb7acec78818d68b762efc869bba2420d82 on Tencent:master.

[smancill]

I fixed issues with the install locations in PR #1454, see commits deecf8c17a9f8df15f59fe58e1b57184b2029a8b and 425c1e755f6ab4ea4f9c27a295a6339270ac1162.

Would that fix the problem? I think using configure_package_config_file is better.

[bastianbeischer]

I fixed issues with the install locations in PR #1454, see commits deecf8c and 425c1e7.

Would that fix the problem? I think using configure_package_config_file is better.

Yes, your PR also fixes the problem.