[llvm-readobj] Fixes malformed json on JSON printed corefiles (#92835)

This patch fixes an issue where, when printing corefile notes with
llvm-readobj as json, the dumper generated llvm formatted output which
isn't valid json. This alters the dumper to, in the NT_FILE, note, dump
properly formatted json data.

Prior to this patch the JSON output was formatted like:
 ```
                "Mapping": [
                  "Start": 4096,
                  "End": 8192,
                  "Offset": 12288,
                  "Filename": "/path/to/a.out"
                ],
 ```
 Whereas now it is formatted as:
  ```
                "Mappings": [
                  {
                    "Start": 4096,
                    "End": 8192,
                    "Offset": 12288,
                    "Filename": "/path/to/a.out"
                  },
  ```
Which is valid. Additionally the LLVM output has changed to match the
structure of the JSON output (i.e. instead of lists of keys it is a list
of dictionaries)

0 files changed, 0 insertions, 0 deletions