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

tests/misc/trunner.nim

@@ -11,6 +11,7 @@ import std/[strformat,os,osproc,unittest]
 from std/sequtils import toSeq,mapIt
 from std/algorithm import sorted
 import stdtest/[specialpaths, unittest_light]
+from std/private/globs import nativeToUnixPath
 
 import "$lib/../compiler/nimpaths"
 
@@ -90,11 +91,7 @@ else: # don't run twice the same test
       removeDir(htmldocsDir)
       let (outp, exitCode) = execCmdEx(cmd)
       check exitCode == 0
-      proc nativeToUnixPathWorkaround(a: string): string =
-        # xxx pending https://github.com/nim-lang/Nim/pull/13265 `nativeToUnixPath`
-        a.replace(DirSep, '/')
-
-      let ret = toSeq(walkDirRec(htmldocsDir, relative=true)).mapIt(it.nativeToUnixPathWorkaround).sorted.join("\n")
+      let ret = toSeq(walkDirRec(htmldocsDir, relative=true)).mapIt(it.nativeToUnixPath).sorted.join("\n")
       let context = $(i, ret, cmd)
       var expected = ""
       case i