[P4_Symbolic] Move CreateSymbolicIrTableEntry to more canonical place, ir.{h,cc}. Rename "SymbolicMatchVariables" to just "SymbolicMatch". Add "symbolic" prefix to table_entry.{h,cc}, since lib is all about symbolic table entries. Eliminate IR getters that do not generalize well from table entries to entities.

[P4_Symbolic] Move CreateSymbolicIrTableEntry to more canonical place, ir.{h,cc}. Rename "SymbolicMatchVariables" to just "SymbolicMatch". Add "symbolic" prefix to table_entry.{h,cc}, since lib is all about symbolic table entries. Eliminate IR getters that do not generalize well from table entries to entities. #4656