Add -vet-explicit-allocators

This vet flag will make it so that allocators must be explicitly used
in places where context.allocator and context.temp_allocator are a
procedure parameter.

The goal of this flag is to prevent using the context.allocator in
cases where a different allocator was meant to be used.
Some code bases default context.allocator to nil/panic allocator
to catch this at runtime. This effectively makes it a compile
time error instead.

src/build_settings.cpp

@@ -305,6 +305,7 @@ enum VetFlags : u64 {
 	VetFlag_Cast            = 1u<<8,
 	VetFlag_Tabs            = 1u<<9,
 	VetFlag_UnusedProcedures = 1u<<10,
+	VetFlag_ExplicitAllocators = 1u<<11,
 
 	VetFlag_Unused = VetFlag_UnusedVariables|VetFlag_UnusedImports,
 
@@ -338,6 +339,8 @@ u64 get_vet_flag_from_name(String const &name) {
 		return VetFlag_Tabs;
 	} else if (name == "unused-procedures") {
 		return VetFlag_UnusedProcedures;
+	} else if (name == "explicit-allocators") {
+		return VetFlag_ExplicitAllocators;
 	}
 	return VetFlag_NONE;
 }