Honor Configuration environment variable in CLI options

[Evangelink]

Addresses the Configuration environment-variable regression in #52358.

Summary

• seed the shared -c/--configuration option from the Configuration environment variable
• ignore empty or whitespace-only environment values
• preserve precedence for an explicit --configuration value
• add parser coverage and an end-to-end MTP solution regression test

This follows the approach suggested in the issue discussion and applies consistently to commands using the shared configuration option. A standalone Platform environment variable remains outside this change because there is no equivalent shared CLI option.

Validation

• build.cmd
• 15 focused dotnet.Tests tests covering CommonOptionsTests and the MTP solution regression scenario

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[Copilot]

Pull request overview

This PR restores/extends CLI behavior so the shared -c/--configuration option can default from the Configuration environment variable (addressing the regression reported in #52358), while ensuring explicit CLI values and /p:Configuration continue to take precedence.

Changes:

• Seed --configuration from the Configuration environment variable and forward it as --property:Configuration=....
• Preserve precedence when --property:Configuration=... is explicitly provided (don’t let the implicit env-derived configuration override it).
• Add parser-level tests and an end-to-end dotnet test regression test for solution execution.

Show a summary per file

File	Description
test/dotnet.Tests/ParserTests/CommonOptionsTests.cs	Adds parser tests validating env-defaulting and precedence rules for configuration forwarding.
test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndRunsTestsWithDifferentOptions.cs	Adds an end-to-end regression test asserting dotnet test honors Configuration env var when --configuration is not passed.
src/Cli/Microsoft.DotNet.Cli.Definitions/Common/CommonOptions.cs	Implements env-based defaulting for --configuration and adds forwarding logic to avoid overriding explicit /p:Configuration.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 1