ObjectMapper: match interfaces with reality

The documented ObjectMapper interfaces do not match the reference
implementation in phosphor-objmgr.  Lots of code currently uses
hand-written dbus calls to the ObjectMapper, using the real interfaces
and not the documented ones.  Refactoring all of these implementations
is quite a bit of effort, which could be staged at a later time (or
leverage a versioned interface).  Update the interface to match reality
so that generated bindings could be leveraged.

Tested:

Ran the reference implementation and compared the signatures with the
YAML and updated as necessary.
```
$ busctl --user introspect xyz.openbmc_project.ObjectMapper /xyz/openbmc_project/object_mapper xyz.openbmc_project.ObjectMapper
NAME                             TYPE      SIGNATURE RESULT/VALUE FLAGS
.GetAncestors                    method    sas       a{sa{sas}}   -
.GetAssociatedSubTree            method    ooias     a{sa{sas}}   -
.GetAssociatedSubTreePaths       method    ooias     as           -
.GetObject                       method    sas       a{sas}       -
.GetSubTree                      method    sias      a{sa{sas}}   -
.GetSubTreePaths                 method    sias      as           -
```

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If6fc6a403d602d6c18c6e30dc1a216a47d059860
diff --git a/yaml/xyz/openbmc_project/ObjectMapper.interface.yaml b/yaml/xyz/openbmc_project/ObjectMapper.interface.yaml
index 9cde19a..c7b8c78 100644
--- a/yaml/xyz/openbmc_project/ObjectMapper.interface.yaml
+++ b/yaml/xyz/openbmc_project/ObjectMapper.interface.yaml
@@ -10,7 +10,7 @@
           given path.
       parameters:
           - name: path
-            type: object_path
+            type: string
             description: >
                 The object path for which the result should be fetched.
           - name: interfaces
@@ -31,7 +31,7 @@
           method.
       parameters:
           - name: path
-            type: object_path
+            type: string
             description: >
                 The path for which the result should be fetched.
           - name: interfaces
@@ -40,7 +40,7 @@
                 An array of result set constraining interfaces.
       returns:
           - name: ancestors
-            type: dict[object_path,dict[string,array[string]]]
+            type: dict[string,dict[string,array[string]]]
             description: >
                 A dictionary of ancestor -> services.
       errors:
@@ -51,7 +51,7 @@
           services is of the type returned by the GetObject method.
       parameters:
           - name: subtree
-            type: object_path
+            type: string
             description: >
                 The subtree path for which the result should be fetched.
           - name: depth
@@ -65,7 +65,7 @@
                 An array of result set constraining interfaces.
       returns:
           - name: objects
-            type: dict[object_path,dict[string,array[string]]]
+            type: dict[string,dict[string,array[string]]]
             description: >
                 A dictionary of path -> services.
       errors:
@@ -75,7 +75,7 @@
           Obtain an array of paths where array elements are in subtree.
       parameters:
           - name: subtree
-            type: object_path
+            type: string
             description: >
                 The subtree path for which the result should be fetched.
           - name: depth
@@ -89,7 +89,7 @@
                 An array of result set constraining interfaces.
       returns:
           - name: paths
-            type: array[object_path]
+            type: array[string]
             description: >
                 An array of paths.
       errors:
@@ -118,7 +118,7 @@
                 An array of result set constraining interfaces.
       returns:
           - name: objects
-            type: dict[object_path,dict[string,array[string]]]
+            type: dict[string,dict[string,array[string]]]
             description: >
                 A dictionary of path -> services.
       errors:
@@ -129,11 +129,11 @@
           association endpoint on associatedPath
       parameters:
           - name: associatedPath
-            type: object_path
+            type: string
             description: >
                 The path where the associated endpoint is fetched from.
           - name: subtree
-            type: object_path
+            type: string
             description: >
                 The subtree path for which the result should be fetched.
           - name: depth
@@ -147,7 +147,7 @@
                 An array of result set constraining interfaces.
       returns:
           - name: paths
-            type: array[object_path]
+            type: array[string]
             description: >
                 An array of paths.
       errors: