Use single file for extends (#3216)

* Use single file for extends

* Update changelog

sass/form/_all.sass

@@ -1,9 +1,9 @@
 /* Bulma Form */
 @charset "utf-8"
 
-@import "shared.sass"
-@import "input-textarea.sass"
-@import "checkbox-radio.sass"
-@import "select.sass"
-@import "file.sass"
-@import "tools.sass"
+@import "shared"
+@import "input-textarea"
+@import "checkbox-radio"
+@import "select"
+@import "file"
+@import "tools"

sass/form/checkbox-radio.sass

@@ -1,5 +1,3 @@
-@import "shared"
-
 %checkbox-radio
   cursor: pointer
   display: inline-block

sass/form/file.sass

@@ -1,5 +1,3 @@
-@import "shared"
-
 $file-border-color: $border !default
 $file-radius: $radius !default
 

sass/form/input-textarea.sass

@@ -1,5 +1,3 @@
-@import "shared"
-
 $textarea-padding: $control-padding-horizontal !default
 $textarea-max-height: 40em !default
 $textarea-min-height: 8em !default

sass/form/select.sass

@@ -1,5 +1,3 @@
-@import "shared"
-
 $select-colors: $form-colors !default
 
 .select

sass/form/tools.sass

@@ -1,5 +1,3 @@
-@import "shared"
-
 $label-color: $text-strong !default
 $label-weight: $weight-bold !default