Made default capacity of dynamic arrays more consistent.

Before this if you do `arr: [dynamic]int` and then append to arr, then it will have capacity 8.
But if you did `arr := make([dynamic]int, context.temp_allocator)` then arr would have capacity 16.

Now both `arr: [dynamic]int` and `arr := make([dynamic]int, context.temp_allocator)` will resut in arr having zero 0. The only reason to use `make` without an explicit len or cap now is because you want to set it up for a non-default allocator. After the first call to `append` it will now in both cases have capacity 8.

I also updated the documentation on the strings builder, both to reflect this, and also to fix it incorrectly saying that len would be 'max(16,len)', which wasn't true even before these changes.

base/runtime/core_builtin_soa.odin

@@ -147,7 +147,7 @@ make_soa_slice :: proc($T: typeid/#soa[]$E, length: int, allocator := context.al
 @(builtin, require_results)
 make_soa_dynamic_array :: proc($T: typeid/#soa[dynamic]$E, allocator := context.allocator, loc := #caller_location) -> (array: T, err: Allocator_Error) #optional_allocator_error {
 	context.allocator = allocator
-	reserve_soa(&array, DEFAULT_RESERVE_CAPACITY, loc) or_return
+	reserve_soa(&array, 0, loc) or_return
 	return array, nil
 }
 
@@ -280,7 +280,8 @@ append_soa_elem :: proc(array: ^$T/#soa[dynamic]$E, arg: E, loc := #caller_locat
 	}
 
 	if cap(array) <= len(array) + 1 {
-		cap := 2 * cap(array) + 8
+		// Same behavior as append_soa_elems but there's only one arg, so we always just add DEFAULT_DYNAMIC_ARRAY_CAPACITY.
+		cap := 2 * cap(array) + DEFAULT_DYNAMIC_ARRAY_CAPACITY
 		err = reserve_soa(array, cap, loc) // do not 'or_return' here as it could be a partial success
 	}
 
@@ -337,7 +338,7 @@ append_soa_elems :: proc(array: ^$T/#soa[dynamic]$E, args: ..E, loc := #caller_l
 	}
 
 	if cap(array) <= len(array)+arg_len {
-		cap := 2 * cap(array) + max(8, arg_len)
+		cap := 2 * cap(array) + max(DEFAULT_DYNAMIC_ARRAY_CAPACITY, arg_len)
 		err = reserve_soa(array, cap, loc) // do not 'or_return' here as it could be a partial success
 	}
 	arg_len = min(cap(array)-len(array), arg_len)