Consider renaming `--output` to `--format` CLI-wide to free `--output` for directory targeting

## Context

From [PR #5535 discussion](https://github.com/Azure/azure-functions-core-tools/pull/5535) — the `func new` redesign needs an option for the template output directory (analogous to `dotnet new --output`), but `--output` / `-o` is already used across v5 commands to control rendering format (plain/json).

Currently `--output` means "format" on:
- `func new`
- `func start`
- `func setup`

This forces the template output directory to use `--path`, which is ambiguous.

## Proposal

Rename the format option from `--output` to `--format` across all commands, then use `--output` / `-o` for directory targeting on `func new` (and potentially `func init`), matching `dotnet new --output` conventions.

## Why now is a good time

- `--output` as format is a v5-only convention — v4 doesn't use it
- v5 is still in preview, so breaking changes are expected
- Aligning with `dotnet new --output` reduces learning curve

## Scope

Needs a CLI-wide audit of `--output` usage and a coordinated rename across all affected commands.

Start by auditing every v5 CLI entry point that uses --output, especially func new, func start, and func setup, and compare the existing option behavior with the proposal. Done means the format option is consistently named --format across affected commands and --output/-o is available for directory targeting where specified, with tests covering the renamed options.

Written by the indexing model from the issue text.