RFR: 8350819: Ignore core files

[Erik Joelsson]

On Wed, 26 Feb 2025 22:26:58 GMT, Mikael Vidstedt <mikael at openjdk.org> wrote:

> Core files may from time to time end up in the source tree of the JDK, adding noise in git etc. Because we have valid files and directories called "core*" in the tree it's non-trivial to exclude any and all core files, but as a special case we can at least ignore `core.[0-9]*` which is the typical format used for linux core files. We don't have any such files/directories at the moment and it's unlikely we ever will.
> 
> Testing:
> 
> * Manually verified that core files are ignored as expected, both in the top directory and in subdirectories
> * tier1 + builds-tier[2-5]

Marked as reviewed by erikj (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/23815#pullrequestreview-2646155008