Revert tree expansion logical changes from SDK modernization commit

[jasonleenaylor]

Reverts behavioral changes in 5711bf6 that were unconnected to the .NET modernization

1. Slice.cs: Restore default-expand behavior (expansion != "doNotExpand") fix LT-22469

[For future PR]
2. StackDumperWin64.cpp: Restore SymGetLineFromAddr64 GetProcAddress loading
3. StackDumper.cpp: Restore real stack capture via SEH in DumpStackHere

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This change is 

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   6m 13s ⏱️ +24s
4 074 tests ±0  4 003 ✅ ±0  71 💤 ±0  0 ❌ ±0 
4 083 runs  ±0  4 012 ✅ ±0  71 💤 ±0  0 ❌ ±0 

Results for commit 214de97. ± Comparison against base commit b6ac397.

♻️ This comment has been updated with latest results.

[jasonleenaylor]

I was also trying to get other changes into this PR initially, but they were harder to tease out. Splitting those into a follow up commit.

[johnml1135]

@johnml1135 reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on jasonleenaylor).

[Copilot]

Pull request overview

Reverts unintended behavioral changes introduced during a .NET modernization commit, restoring prior UI tree expansion behavior and (per description) native stack dumping behavior.

Changes:

• Restores default-expand behavior for slices unless explicitly marked doNotExpand.
• (Per PR description) restores prior symbol line loading and SEH-based stack capture in stack dump components.

[Copilot]

The string literal "doNotExpand" is a protocol value that’s easy to mistype and hard to discover/refactor. Consider centralizing it as a named constant (or using an enum-like pattern) and, if this value is intended to be case-insensitive in XML, using an explicit StringComparison to make that contract clear.

Suggested change

	bool fExpand = XmlUtils.GetOptionalAttributeValue(node, "expansion") != "doNotExpand";
	const string DoNotExpandExpansionValue = "doNotExpand";
	bool fExpand = XmlUtils.GetOptionalAttributeValue(node, "expansion") != DoNotExpandExpansionValue;