Report install errors and failures in JSON format

[Vishvendra47]

This PR addresses issue #11316 by ensuring that when pip install is executed with the --report option, any installation or dependency resolution errors are outputted in JSON format instead of terminating with plain text logs on stdout.

Changes

1. src/pip/_internal/commands/install.py:
   • Initialized requirement_set = None before the installation try-block.
   • Added a dedicated exception handler for (InstallationError, CommandError, InstallWheelBuildError).
   • If --report is specified, the handler creates an InstallationReport (with whatever requirements were parsed up to that point), converts it to a dictionary, injects an error dictionary containing code (the exception class name) and description (the error message), outputs it (to stdout or a file), and then re-raises the exception.
2. tests/functional/test_install_report.py:
   • Added test_install_report_error and test_install_report_error_stdout to verify the error reporting output.
3. News Fragment:
   • Added news/11316.feature.rst news fragment file.

Output Example

Running pip install "pip-tools==6.8.0" "pip==20.1" --dry-run --report - now outputs:

{
  "version": "1",
  "pip_version": "26.2.dev0",
  "install": [],
  "environment": { ... },
  "error": {
    "code": "DistributionNotFound",
    "description": "ResolutionImpossible: ..."
  }
}

[Vishvendra47]

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