Execute(|Script)Plugin entry names: QString => const char[]

The initialization of these static data members is now static rather
than dynamic. Thus the possibility of static initialization order fiasco
and other issues with global variables are eliminated.

These strings are used only as KConfigGroup keys.
KConfigGroup::(read|write)Entry() overloads that take const QString& key
convert the QString argument to const char*. So this change is
beneficial to performance.

Move several constants from ExecutePlugin to its base class
IExecutePlugin in order to reuse them in debugger tests instead of
duplicating string literals.

1 job for !203 with const-config-entry-names in 33 minutes and 2 seconds (queued for 100 minutes and 23 seconds)
Status Job ID Name Coverage
passed #83524
linux kf5-qt5 qt5.15