Enhancements:
-------------

* Add CLI flag (--merge-build-host) to restore pre-3.1.4 behavior with merging build and host envs  #26260

Bug fixes:
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* Check recipe/metadata skip status in more places, rather than strictly at the top-level  #2617
* fix unnecessary conforming of zip keys when distributing variants  #2618
* fix matching of unrendered output names when matching rendered names  #2618
* fix matching of partial (only used parts) of variants when lining up subpackages  #2618
* fix handling of outputs with same name as top level when considering used vars  #2618
* exclude top-level run_exports from applying to all outputs  #2618
* Fix linking compiler runtimes from build to host prefix (was broken by build/host prefix split in 3.1.4)  #2621
* Fix logic errors around merging build/host envs  #2623
* fix run_exports in outputs being overwritten  #2623