Improve code examples in writing-an-exception-filter.md

[jeremy-rifkin]

This PR is primarily a formatting PR. I recognize that style is highly subjective, however, I am opening this PR because I find the formatting in writing-an-exception-filter.md to be confusing and more importantly inconsistent.

This PR:

• Moves function forward-declarations outside of other function bodies
• Formats empty compound statements more consistently
• Formats spacing in parentheses consistently (I find __except ( Eval_Exception( GetExceptionCode( ))) especially egregious formatting)
• Uses 4-space indentation instead of 3-space
• Indents control flow bodies

The one substantive change I made is changing ResetVars to a more general HandleOverflow function, as I found the purpose of ResetVars misleading in this example.

In preparing this PR I consulted the style guide and in absense of clear code formatting guidelines I looked to other well-formatted articles, such as Modern C++ best practices for exceptions and error handling.

[prmerger-automator]

@jeremy-rifkin : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit 3704b28:

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PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.

[learn-build-service-prod]

Learn Build status updates of commit bde53f9:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/cpp/writing-an-exception-filter.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.

[ShannonLeavitt]

@TylerMSFT

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[TylerMSFT]

Hi, I'm not a fan of the old formatting or the new formatting. We changed our style for braces to be on their own lines as one example. But I think this is an improvement and particularly the change from ResetVars() to HandleOverflow() is better. Thank you.

[TylerMSFT]

#sign-off

[jeremy-rifkin]

Thanks Tyler for the quick response and merge. Are there any code style guidelines written down for the microsoft docs?

[TylerMSFT]

not that I'm aware of for the c++ docs.