`install(TARGETS)` does not install the `HEADERS` `FILE_SET` by default

The documentation page for the install(TARGETS ...) command lists FILE_SET (specifically HEADERS) has a default install location, but currently the HEADERS FILE_SET is not installed.

This causes problems when exporting the target/project since cmake will error out with: install TARGETS target repro is exported but not all of its interface file sets are installed (minimal repro at the end)

This makes it kinda manditory to specify all ARCHIVE/RUNTIME/... parts and locations (possibly even COMPONENT) that should be installed instead of simply specifying which targets to install and cmake picking sane defaults.

cmake_minimum_required(VERSION 3.23)

project(repro)

add_library(${PROJECT_NAME} STATIC)

target_sources(${PROJECT_NAME} PRIVATE lib.cpp)
target_sources(${PROJECT_NAME} PUBLIC FILE_SET HEADERS FILES lib.hpp)

install(TARGETS ${PROJECT_NAME} EXPORT ${PROJECT_NAME}Export)

include(GNUInstallDirs)
include(CMakePackageConfigHelpers)

install(
	EXPORT ${PROJECT_NAME}Export
	DESTINATION lib/cmake/${PROJECT_NAME}
	NAMESPACE ${PROJECT_NAME}::
)