[feature][PkgConfigDeps] Warn about duplicated *.pc names

[franramirez688]

Changelog: Feature: PkgConfigDeps shows WARN messages if there are duplicated pkg_config_name and/or pkg_config_aliases.
Docs: conan-io/docs#2378
Closes #10226

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[memsharded]

Looking good, maybe a bit of repetition in the warn msg that could be refactored later, but good atm.