Firefox: Document or automate displaying WPT test section headers as hunk headers in Git diffs

[ErichDonGubler]

With the following .gitconfig snippet:

[diff "wpt-metadata"]
	xfuncname = "^\\[.*\\]\\s*$"

…and the following .gitattributes snippet:

testing/web-platform/meta/**/*.ini diff=wpt-metadata
testing/web-platform/mozilla/meta/**/*.ini diff=wpt-metadata

…git diff can yield output like this when run in a Git checkout of Gecko:

diff --git a/testing/web-platform/mozilla/meta/webgpu/chunked/20/cts.https.html.ini b/testing/web-platform/mozilla/meta/webgpu/chunked/20/cts.https.html.ini
index b51d7fe6de28a..ea93b2101d342 100644
--- a/testing/web-platform/mozilla/meta/webgpu/chunked/20/cts.https.html.ini
+++ b/testing/web-platform/mozilla/meta/webgpu/chunked/20/cts.https.html.ini
@@ -48,6 +48,7 @@ [cts.https.html?q=webgpu:api,validation,encoding,cmds,setBindGroup:dynamic_offse
   [:encoderType="compute%20pass";dynamicOffsets=[\];useU32array=true]
     expected:
       if os == "mac": FAIL
+      blarg
 
   [:encoderType="compute%20pass";dynamicOffsets=[512,0\];useU32array=false]
     expected:

The exciting part is the hunk header output that's showing the test section header a few dozen lines up in source (!):

@@ -48,6 +48,7 @@ [cts.https.html?q=webgpu:api,validation,encoding,cmds,setBindGroup:dynamic_offse

…which we didn't have before. 🙂

[ErichDonGubler]

Automation for the Git config. portion of OP might be possible with GIT_CONFIG_* env. vars (see git/git:b3b186262:git-config.txt:355-365) or git -c.

[ErichDonGubler]

Settings attributes and config. might be possible through the gix crate's Repository::attributes_only API (which wraps the gix-attributes crate).