fix: ensure output.distPath can be merged correctly

[chenjiahan]

Summary

This PR moves the normalizeConfigStructure helper to the merge Rsbuild configuration phase, ensuring that the output.distPath config can be merged correctly. See the newly added test cases for details.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[Copilot]

Pull Request Overview

This PR refactors configuration normalization to ensure proper merging of output.distPath when specified as a string. The change moves the normalizeConfigStructure logic from the initialization phase into the merge phase, allowing configuration properties like output.distPath and output.copy to be normalized before merging rather than after.

Key Changes

• Moved normalizeConfigStructure function from defaultConfig.ts to mergeConfig.ts and integrated it into the merge process
• Removed special-case handling for output.copy from the merge function since normalization now handles structure consistency
• Updated initConfigs.ts and normalizeConfig to use the new normalization approach

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
packages/core/tests/mergeConfig.test.ts	Added test cases verifying correct merging behavior for output.copy and output.distPath configurations
packages/core/src/provider/initConfigs.ts	Removed normalizeConfigStructure import and call since normalization now happens during merge
packages/core/src/mergeConfig.ts	Added normalizeConfigStructure function and integrated it into mergeRsbuildConfig to normalize configs before merging
packages/core/src/defaultConfig.ts	Removed normalizeConfigStructure function and moved publicDir normalization logic into normalizeConfig

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[Copilot]

Pull Request Overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

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