refactor(compiler): move variable optimization earlier in pipeline (angular#55771)

Currently the variable optimization phase happens somewhat late in the process which is okay since the variables are generally static (e.g. `reference()` instruction calls). In some upcoming work we'll have variables that consume slots and require `advance` instructions. To allow for them to be optimized correctly, we need to move the variable optimization phase earlier, at least before we allocate the slots.

PR Close angular#55771

Author: crisbeto

packages/compiler/src/template/pipeline/src/emit.ts

@@ -136,6 +136,7 @@ const phases: Phase[] = [
   {kind: Kind.Both, fn: generateNullishCoalesceExpressions},
   {kind: Kind.Both, fn: expandSafeReads},
   {kind: Kind.Both, fn: generateTemporaryVariables},
+  {kind: Kind.Both, fn: optimizeVariables},
   {kind: Kind.Tmpl, fn: allocateSlots},
   {kind: Kind.Tmpl, fn: resolveI18nElementPlaceholders},
   {kind: Kind.Tmpl, fn: resolveI18nExpressionPlaceholders},
@@ -147,7 +148,6 @@ const phases: Phase[] = [
   {kind: Kind.Tmpl, fn: removeI18nContexts},
   {kind: Kind.Both, fn: countVariables},
   {kind: Kind.Tmpl, fn: generateAdvance},
-  {kind: Kind.Both, fn: optimizeVariables},
   {kind: Kind.Both, fn: nameFunctionsAndVariables},
   {kind: Kind.Tmpl, fn: resolveDeferDepsFns},
   {kind: Kind.Tmpl, fn: mergeNextContextExpressions},