--Update/cleanup gitignore

[jturner65]

Motivation and Context

Small update to git ignore :

• Remove ancient references to semantic test assets
• Reorganize /data/ ignore pattern - ignore everything in data except currently specified directories and files. This is to facilitate development, while also requiring any additions to the /data/` to be explicitly specified (since data should be accessed via the downloader and stored elsewhere)
• Add ignore for local src/test/configure.h shortcut for gitkraken users :) (which does not support .git/info/exclude specifications)

How Has This Been Tested

Via git access

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.

[0mdc]

LGTM!