public Map<Integer, ExecutableRecord> generateExecutableXrefMap() {
		TreeMap<Integer, ExecutableRecord> treeMap = new TreeMap<>();
		int xrefIndex = 1;
		for (ExecutableRecord exe : exerec) {
			exe.setXrefIndex(xrefIndex);
			treeMap.put(xrefIndex, exe);
			xrefIndex += 1;
		}
		return treeMap;
	}
Assign an internal id to all executables and also create a map from id to executable.
As with {@link DescriptionManager#populateExecutableXref},
ids are assigned in order starting at 1
@return the populated Map object
Ghidra/Features/BSim/src/main/java/ghidra/features/bsim/query/description/DescriptionManager.java