Define new Pre-/PostEscapeAnalysis optimizations

Added enum definitions for preEscapeAnalysis and postEscapeAnalysis, in
preparation for a new J9 optimization that is pending.

Submitting on behalf of Andrew Craik <ajcraik@ca.ibm.com>

Signed-off-by:  Henry Zongaro <zongaro@ca.ibm.com>

compiler/optimizer/OMROptimizations.enum

@@ -49,7 +49,9 @@
    OPTIMIZATION(partialRedundancyElimination)
    OPTIMIZATION(globalCopyPropagation)
    OPTIMIZATION(globalDeadStoreElimination)
+   OPTIMIZATION(preEscapeAnalysis)
    OPTIMIZATION(escapeAnalysis)
+   OPTIMIZATION(postEscapeAnalysis)
    OPTIMIZATION(isolatedStoreElimination)
    OPTIMIZATION(deadTreesElimination)
    OPTIMIZATION(redundantGotoElimination)