refs #21621 [finc] vf6: breaks down SCSS into meaningful chunks

* removes javascript type references in finc
* re-instates bulk-action-buttons template for proper id assignment and display
* SCSS separation
* removes javascript type references in finc
* re-instates bulk-action-buttons template for proper id assignment and display
* continues SCSS separation
* clarifies keep filter elements (partial move to finc theme)
* increases touch/click area on keep filters

* bootstrap3 VF6.x to VF 8.1: adds missing !default flags to accessibility.scss
** attempt to get this fixes is in PR https://github.com/vufind-org/vufind/pull/2483

co-authored by: Robert Lange <robert.lange@uni-leipzig.de>