fix: gf fails on "foo/bar.txt:1:2" on Windows

Problem:
On Windows, "gf" fails on a filepath that has a line:column suffix.
Example:

    E447: Can't find file "src/app/core/services/identity/identity.service.ts:64:23"

Solution:
- Remove ":" from 'isfname' on Windows. Colon is not a valid filename
  character (except for the drive-letter).
- Handle drive letters specially in file_name_in_line().

Fixes #25160

test/old/testdir/setup.vim

@@ -26,6 +26,9 @@ if exists('s:did_load')
   set sessionoptions+=options
   set viewoptions+=options
   set switchbuf=
+  if has('win32')
+    set isfname+=:
+  endif
   if g:testname !~ 'test_mapping.vim$'
     " Make "Q" switch to Ex mode.
     " This does not work for all tests.