Fix T64573: RNA_path_from_ID_to_property fails for pointcaches

Give pointcaches a proper path function which e.g. also resolves
ALT+click (assign to all selected) not working for anything relating to
pointcaches.

This also cleans up the usage of the 'eModifierTypeFlag_UsesPointCache'
flag (removed from the boolean modifier, added to the softbody modifier).

Maniphest Tasks: T64573

Differential Revision: https://developer.blender.org/D7115

source/blender/modifiers/intern/MOD_boolean.c

@@ -351,7 +351,7 @@ ModifierTypeInfo modifierType_Boolean = {
     /* structName */ "BooleanModifierData",
     /* structSize */ sizeof(BooleanModifierData),
     /* type */ eModifierTypeType_Nonconstructive,
-    /* flags */ eModifierTypeFlag_AcceptsMesh | eModifierTypeFlag_UsesPointCache,
+    /* flags */ eModifierTypeFlag_AcceptsMesh,
 
     /* copyData */ modifier_copyData_generic,