In a large soup or stockpot combine the chicken pieces, chicken necks, ginger, crushed scallions, smashed garlic and 4 quarts of water and bring to a boil over high heat. Reduce the heat to a simmer and cook until the chicken is fall-from-the-bone-tender, 1 to 1 1/2 hours. Strain the liquid through a fine-mesh sieve and set the chicken pieces aside to cool. Skim and discard any foam or fat that has accumulated on the top of the broth and add water, if needed, to bring the volume back up to 4 quarts. Discard the chicken necks and other solids. Return the chicken broth to the soup pot and add the rice. Return the pot to a boil, reduce the heat to a simmer, and cook, stirring frequently, until the rice is completely broken down and the liquid has thickened to a porridge-like consistency, about 2 1/2 hours. (Note: take care during the last half hour of cooking that the soup does not scorch on the bottom. Reduce the heat if necessary and stir often.) The soup should be porridge-like consistency - but if it becomes too thick, add a bit of water as necessary.
While the soup is cooking, remove the chicken meat from the bones once it has cooled and shred the meat into bite size pieces. Reserve. Discard skin and bones.
Heat 2 inches of oil in a medium saucepan and, when hot, fry the shallots until crispy, about 2 minutes. Remove from the oil and transfer to paper-lined plate to drain. Repeat the same process with the sliced garlic - it should cook in about 1 minute -- and set aside.
When the soup is ready, serve in shallow bowls, with small bowls of each garnish available so that guests can garnish their soup as desired -- with the crispy shallots, crispy garlic, chopped cilantro, sliced scallions, fish sauce, soy sauce and sesame oil each added to individual taste. Garnish each bowl with a lime wedge. Serve immediately.