walkDirRecFilter, update doc CI filter, compiler/index.nim for docs + various other fixes (#14501)

* update doc CI filter to include the files mostly likely to require doc rebuild
* remove code duplication in ./config/nimdoc.cfg; show link to compiler docs, various fixes
* walkDirRecFilter, factor nativeToUnixPath workaround
* glob for getRst2html
* docslocal: 40s to build all docs
* revert code dedup in github actions which did not work alas...
* fixups

.github/workflows/ci_docs.yml

@@ -1,18 +1,27 @@
 name: Nim Docs CI
 on:
   push:
-    # Run only on changes on these files
     paths:
-      - 'lib/**.nim'
+      - 'compiler/docgen.nim'
+      - 'compiler/renderverbatim.nim'
       - 'doc/**.rst'
       - 'doc/nimdoc.css'
+      - 'lib/**.nim'
+      - 'nimdoc/testproject/expected/testproject.html'
+      - 'tools/dochack/dochack.nim'
+      - 'tools/kochdocs.nim'
       - '.github/workflows/ci_docs.yml'
-
   pull_request:
     # Run only on changes on these files
     paths:
-      - 'lib/**.nim'
+      - 'compiler/docgen.nim'
+      - 'compiler/renderverbatim.nim'
       - 'doc/**.rst'
+      - 'doc/nimdoc.css'
+      - 'lib/**.nim'
+      - 'nimdoc/testproject/expected/testproject.html'
+      - 'tools/dochack/dochack.nim'
+      - 'tools/kochdocs.nim'
       - '.github/workflows/ci_docs.yml'
 
 jobs:
@@ -115,13 +124,6 @@ jobs:
         shell: bash
         run: ./koch doc --git.commit:devel
 
-      - name: 'Prepare documentation for deployment'
-        if: |
-          github.event_name == 'push' && github.ref == 'refs/heads/devel' &&
-          matrix.target == 'linux'
-        shell: bash
-        run: cp -f doc/html/{overview,index}.html
-
       - name: 'Publish documentation to Github Pages'
         if: |
           github.event_name == 'push' && github.ref == 'refs/heads/devel' &&