[release/9.0-staging] [mono] Fix crash while debugging AOT'ed app.

[github-actions]

Backport of #117627 to release/9.0-staging

/cc @thaystg

Customer Impact

• Customer reported
• Found internally

We initially backported this change to 10, but held off because there were no reported issues with .NET 9. That has changed with https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2604939 where we were able to reproduce the issue.

The change fixes a crash in debugger by adding a null check around TLS data before dereferencing a pointer.

Regression

• Yes
• No

[If yes, specify when the regression was introduced. Provide the PR or commit if known.]

Testing

Manually tested a default iOS SDK application

Risk

Low

IMPORTANT: If this backport is for a servicing release, please verify that:

• The PR target branch is release/X.0-staging, not release/X.0.

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

[tarekgh]

@thaystg I marked this PR with the servicing consider label till you get the tactics approval.

[PranavSenthilnathan]

Reminder that PRs into release/9.0-staging need to be completed by 4pm Redmond time on October 13 to make it into the November servicing release. After that point you'll need to target release/9.0 if you want to make the November release.