Upgrade bundled Expat to 2.7.5 (e.g. for the fixes to `CVE-2026-3277{6,7,8}`)

[StanFromIreland]

See https://blog.hartwork.org/posts/expat-2-7-5-released/ for more information on the release.

Linked PRs

• gh-146083: Upgrade bundled Expat to 2.7.5 #146085
• [3.14] gh-146083: Upgrade bundled Expat to 2.7.5 (GH-146085) #146603
• [3.13] gh-146083: Upgrade bundled Expat to 2.7.5 (GH-146085) #146604
• [3.12] gh-146083: Upgrade bundled Expat to 2.7.5 (GH-146085) #146605
• [3.11] gh-146083: Upgrade bundled Expat to 2.7.5 (GH-146085) #146607
• [3.10] gh-146083: Upgrade bundled Expat to 2.7.5 (GH-146085) #146608