Improving responsive grid xml parser

Refactors AllAppsSpecs, FolderSpecs and WorkspaceSpecs initialization to use the same code to parse the xml with different map function. This CL improves the readability of the code and remove code duplication.

Fix: 286538013
Flag: ENABLE_RESPONSIVE_WORKSPACE
Test: AllAppsSpecsTes
Test: CalculatedAllAppsSpecTest
Test: CalculatedFolderSpecsTest
Test: CalculatedWorkspaceSpecTest
Test: FolderSpecsTest
Test: WorkspaceSpecsTest
Test: DeviceProfileResponsiveDumpTest
Test: DeviceProfileResponsiveAlternativeDisplaysDumpTest
Change-Id: Iec5863619399efd2e80f3db46b75c4d785e1656f