This reverts commit a988fad9a0.
As discussed in #57725 and clarified in #57788, `SNAME` is not meant to be used
everywhere but only in critical code paths. For theme methods specifically, it
was by design that only getters use `SNAME` and not setters.
* Added a new macro SNAME() that constructs and caches a local stringname.
* Subsequent usages use the cached version.
* Since these use a global static variable, a second refcounter of static usages need to be kept for cleanup time.
* Replaced all theme usages by this new macro.
* Replace all signal emission usages by this new macro.
* Replace all call_deferred usages by this new macro.
This is part of ongoing work to optimize GUI and the editor.
