fix: address feedback

Author: crisbeto

src/lib/button-toggle/button-toggle.scss

@@ -1,6 +1,6 @@
 @import '../core/a11y/a11y';
 @import '../core/style/elevation';
-@import '../core/style/prefixes';
+@import '../core/style/vendor-prefixes';
 @import '../core/style/layout-common';
 
 $mat-button-toggle-padding: 0 16px !default;

src/lib/core/option/_option.scss

@@ -1,5 +1,5 @@
 @import '../style/menu-common';
-@import '../style/prefixes';
+@import '../style/vendor-prefixes';
 @import '../a11y/a11y';
 
 /**

src/lib/core/style/_button-common.scss

@@ -1,4 +1,4 @@
-@import './prefixes';
+@import './vendor-prefixes';
 
 // Mixin overriding default button styles like the gray background, the border, and the outline.
 @mixin mat-button-reset {

src/lib/core/style/_prefixes.scss renamed to src/lib/core/style/_vendor-prefixes.scss

@@ -6,7 +6,7 @@
   user-select: none;
 }
 
-@mixin placeholder {
+@mixin input-placeholder {
   &::placeholder {
     @content;
   }

src/lib/input/input-container.scss

@@ -1,5 +1,5 @@
 @import '../core/style/variables';
-@import '../core/style/prefixes';
+@import '../core/style/vendor-prefixes';
 @import '../core/style/form-common';
 
 
@@ -110,7 +110,7 @@ $mat-input-underline-disabled-background-image:
   // Note that we can't use something like visibility: hidden or
   // display: none, because IE ends up preventing the user from
   // focusing the input altogether.
-  @include placeholder {
+  @include input-placeholder {
     color: transparent;
   }
 }

src/lib/select/select.scss

@@ -2,7 +2,7 @@
 @import '../core/style/list-common';
 @import '../core/style/form-common';
 @import '../core/style/variables';
-@import '../core/style/prefixes';
+@import '../core/style/vendor-prefixes';
 @import '../core/a11y/a11y';
 
 $mat-select-trigger-height: 30px !default;

src/lib/slide-toggle/slide-toggle.scss

@@ -1,7 +1,7 @@
 @import '../core/style/variables';
 @import '../core/ripple/ripple';
 @import '../core/style/elevation';
-@import '../core/style/prefixes';
+@import '../core/style/vendor-prefixes';
 @import '../core/a11y/a11y';
 
 $mat-slide-toggle-thumb-size: 20px !default;

tools/stylelint/no-prefixes/needs-prefix.js

@@ -3,8 +3,10 @@ const Browsers = require('autoprefixer/lib/browsers');
 const Prefixes = require('autoprefixer/lib/prefixes');
 
 /**
- * Utility to be used when checking whether a CSS declaration needs to be prefixed.
- * Based on https://github.com/stylelint/stylelint/blob/master/lib/utils/isAutoprefixable.js
+ * Utility to be used when checking whether a CSS declaration needs to be prefixed. Based on
+ * Stylelint's `no-vendor-prefix` rule, but instead of checking whether a rule has a prefix,
+ * we check whether it needs one.
+ * Reference https://github.com/stylelint/stylelint/blob/master/lib/utils/isAutoprefixable.js
  */
 module.exports = class NeedsPrefix {
   constructor(browsers) {