Deduplicate 'already installed' / HEAD message.

[BillyONeal]

Improve console output when installing packages by deduplicating 'already installed' message, --head warning, and merging the 'green success' message into the total elapsed time part.

Cherry picked from #1514

Normal:

--head:

[Copilot]

Pull Request Overview

This PR deduplicates console output for installed packages and refactors related message formatting to clearly separate --head warnings from normal output while merging the success message into the total elapsed time display.

• Introduces a new all_text() method in FormattedPlan to combine warning and normal texts.
• Renames InstallSummary::format() to format_results() and replaces the failed() method with a print_complete_message() for clearer failure reporting.
• Updates tests, message strings, and related pipelines to validate the improved output formatting.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/vcpkg/dependencies.cpp	Added all_text() and updated plan block usage for deduplicated messages.
src/vcpkg/commands.upgrade.cpp	Updated to use summary.format_results() and print_complete_message().
src/vcpkg/commands.set-installed.cpp	Refactored lambda to update install_actions to already_installed actions.
src/vcpkg/commands.install.cpp	Renamed format(), adjusted summary failure handling and print messages.
src/vcpkg/commands.ci.cpp	Updated to use summary.format_results() for consistent output.
src/vcpkg-test/dependencies.cpp	Modified tests to validate the new all_text() output.
locales/messages.json	Updated messages to reflect changes in wording for installed packages.
include/vcpkg/dependencies.h	Updated structure with new members and all_text() declaration.
include/vcpkg/commands.install.h	Renamed format() and removed the failed() method in favor of new printing API.
include/vcpkg/base/message-data.inc.h	Revised message definitions for clearer already installed and elapsed time messaging.
azure-pipelines/end-to-end-tests-dir/build-test-ports.ps1	Adapted test expectations for the updated --head message output.