docs: Improve transform-docs.awk with multi-line tag buffering and update broken files list

copy-upstream-docs.sh

@@ -23,45 +23,17 @@ LOCAL_FILES="
 # Files that are not valid MDX syntax
 # This output pasted from a CI job - we should burn it down to zero
 BROKEN_FILES="
-community/roadmaps-configurability.mdx
-community/users.mdx
-concepts/build-files.mdx
-concepts/dependencies.mdx
-concepts/labels.mdx
-configure/integrate-cpp.mdx
-configure/windows.mdx
-contribute/search.mdx
-docs/cc-toolchain-config-reference.mdx
-docs/mobile-install.mdx
-docs/user-manual.mdx
-extending/config.mdx
-extending/legacy-macros.mdx
-extending/macros.mdx
-external/extension.mdx
-external/faq.mdx
-external/migration.mdx
-external/mod-command.mdx
-external/overview.mdx
-external/registry.mdx
-external/vendor.mdx
-install/windows.mdx
-query/guide.mdx
-query/language.mdx
-query/quickstart.mdx
-reference/flag-cheatsheet.mdx
-reference/test-encyclopedia.mdx
-reference/command-line-reference.mdx
-reference/be/be-nav.mdx
-reference/be/functions.mdx
-reference/be/platforms-and-toolchains.mdx
-release/rolling.mdx
-remote/ci.mdx
-remote/dynamic.mdx
-rules/language.mdx
-rules/windows.mdx
-run/build.mdx
-start/go.mdx
-tutorials/ccp-toolchain-config.mdx
+    concepts/build-files.md
+    concepts/dependencies.md
+    concepts/labels.md
+    configure/windows.md
+    contribute/search.md
+    docs/cc-toolchain-config-reference.md
+    docs/user-manual.md
+    query/quickstart.md
+    reference/flag-cheatsheet.md
+    reference/test-encyclopedia.md
+    run/build.md
 "
 
 # Verify that at least one source exists