Byproducts: Add test for collapsing of full paths in byproducts

Add test for collapsing of full paths in byproducts and additional tests for
the GENERATED source file properties set by add_custom_command and
add_custom_target with relative paths.
22 jobs for byproduct-collapse-full-path
Status Job ID Name Coverage
  External
passed cdash

passed cmake-dash3win10-windows-release-ninja

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passed cmake-hythloth-linux-debug-makefiles+sphinx

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passed cmake-minoc-linux-release-lint-iwyu-tidy

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passed cmake-moonshade-osx-debug-ninja

00:12:12

passed cmake-moonshade-osx-release-makefiles

00:13:54

passed cmake-terfin-windows-release-vs2019

00:46:32

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