Fix newline handling in file, softlink, and ImportLink template functions

Use state-based routing instead of sentinel strings, so whitespace-trimming
syntax (e.g. `{{- file "name" -}}`) correctly creates all named files and
symlinks.

Fixes: #2118

Signed-off-by: Jonathon Anderson <janderson@ciq.com>
Co-authored-by: Christian Goll <cgoll@suse.com>
Signed-off-by: Jonathon Anderson <janderson@ciq.com>

overlays/localtime/internal/localtime_test.go

@@ -52,5 +52,5 @@ func Test_localtimeOverlay(t *testing.T) {
 const localtime string = `backupFile: true
 writeFile: true
 Filename: etc/localtime
-{{ /* softlink "/usr/share/zoneinfo/GMT" */ }}
+Symlink: /usr/share/zoneinfo/GMT
 `