Fix arg annotations when running in IDE mode

[JamesNK]

Description

Apply behavior from https://github.com/dotnet/aspire/blob/main/docs/specs/IDE-execution.md#launch-profile-processing-project-launch-configuration when displaying args in the dashboard.

Two changes:

1. When projects are executed by the IDE, the launch args and app host args aren't merged together. Launch args are only displayed if there are no app host args.
2. If there are no args then project.Spec.Args is left as null. That wasn't happening but appears to have special behavior according to the IDE execution spec. Maybe something along the toolchain automatically converts an empty array to null?

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Is this introducing a breaking change?
      • Yes
        • Link to aspire-docs issue (please use this breaking-change template):
      • No
        • Link to aspire-docs issue (please use this doc-idea template):
  • No

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

tests/Aspire.Hosting.Tests/Dcp/DcpExecutorTests.cs:158

• Slicing exe.Spec.Args without verifying its initialization can lead to a null reference exception when executionType is not IDE. Please ensure that exe.Spec.Args is non-null before attempting to slice it.

var callArgs = executionType == ExecutionType.IDE ? exe.Spec.Args : exe.Spec.Args![^(expectedArgs?.Length ?? 0)..];

tests/Aspire.Hosting.Tests/Dcp/DcpExecutorTests.cs:121

• [nitpick] The parameter 'executionType' is being compared to ExecutionType.IDE, which may be of a different type than string. Consider aligning the types (for example, by using an enum consistently) to improve clarity and avoid potential type conversion issues.

if (executionType == ExecutionType.IDE)

[JamesNK]

@captainsafia I think this change removes the need for #7683. Can probably revert it after merge.

[captainsafia]

Not an expert but LGTM overall -- it does appear that the double --port fix can be reverted with this change set.

[adamint]

just that one question

[karolz-ms]

nice

[danmoseley]

/backport to release/9.1

[github-actions]

Started backporting to release/9.1: https://github.com/dotnet/aspire/actions/runs/13444068467

[JamesNK]

/backport to release/9.1

[github-actions]

Started backporting to release/9.1: https://github.com/dotnet/aspire/actions/runs/13446883474