extension unification ignore settings validation

[benibenj]

This is the only way I could come up with which would support both extensions contributing the same configuration and being able to write to them when either one or both are enabled.

https://github.com/microsoft/vscode-internalbacklog/issues/6073

[Copilot]

Pull Request Overview

This PR introduces a mechanism to bypass validation for certain configuration settings during extension unification. It creates an allowlist of settings (stored in IGNORE_VALIDATION_SETTINGS) that can skip validation checks that would normally reject unknown or duplicate settings.

• Adds IGNORE_VALIDATION_SETTINGS set to bypass validation for specific settings from product configuration
• Updates configuration editing and extension point validation to check this allowlist before rejecting settings
• Temporarily allows settings defined in product.defaultChatAgent.completionsEnablementSetting to bypass validation

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/vs/workbench/services/configuration/common/configuration.ts	Defines the IGNORE_VALIDATION_SETTINGS set populated from product configuration, with a temporary comment indicating removal after extension unification
src/vs/workbench/services/configuration/common/configurationEditing.ts	Adds validation bypass check for settings in the ignore list when validating configuration keys
src/vs/workbench/api/common/configurationExtensionPoint.ts	Skips validation warnings and duplicate property checks for settings in the ignore list during extension point registration

[benibenj]

PR is not ready, but open to different ideas if someone has a better approach

[benibenj]

I considered a different approach which would allow two extensions to contribute the same configuration in a proper manner, however, that adds a ton of complexity and adds risks of causing a regression. As this would only lead to a small improvement I prefer to keep this less nice but simpler approach

[benibenj]

Remove this one in #274797