Adds support for "symbolic" components, which represent feature-level
capabilities of a package that do not correspond to actual build targets.
These are modeled as pseudo-targets, using the INTERFACE type as a base,
and can be queried via:
get_target_property(... <tgt> "SYMBOLIC")
This enables consumers to declare requirements on optional features
(e.g., SSL support) even when they do not map to concrete targets.
Fixes: #27187
Add import/export support and documentation for the SPDX_LICENSE
target property. A target's license can be specified by setting
this property to an SPDX license expression. CMake and CPS-format
export files generated with `export()` or `install()` will
retain the license information. CMake also imports the license
property for imported targets.
Closes: #26706
Refactoring in commit 8c65b7042e (cmExportFileGenerator: Simplify
collection of targets missing from export set, 2022-04-11,
v3.24.0-rc1~281^2) accidentally dropped the behavior change from
commit 0ad2a1c181 (Export: Never treat private link libraries as
public package dependencies., 2013-09-24, v3.0.0-rc1~559^2).
Restore the behavior and add a test.
Fixes: #23838
