feat: add link button

Author: tangjinzhou

components/button/style/index.less

@@ -9,6 +9,17 @@
 @btn-ghost-bg: transparent;
 @btn-ghost-border: @border-color-base;
 
+.btn-link() {
+  .button-variant-other(@primary-color, transparent, transparent);
+  box-shadow: none;
+  &:hover,
+  &:focus,
+  &:active {
+    border-color: transparent;
+  }
+  .button-disabled(@disabled-color; transparent; transparent);
+}
+
 // Button styles
 // -----------------------------
 .@{btn-prefix-cls} {
@@ -69,6 +80,10 @@
     .btn-danger;
   }
 
+  &-link {
+    .btn-link;
+  }
+
   &-round {
     .btn-round(@btn-prefix-cls);
   }
@@ -162,6 +177,11 @@
     .button-variant-ghost(@btn-danger-color);
   }
 
+  &-background-ghost&-link {
+    .button-variant-ghost(@primary-color; transparent);
+    color: @component-background;
+  }
+
   &-two-chinese-chars::first-letter {
     letter-spacing: 0.34em;
   }

components/button/style/mixin.less

@@ -7,7 +7,7 @@
   border-radius: @border-radius;
 }
 
-.button-disabled() {
+.button-disabled(@color: @btn-disable-color; @background: @btn-disable-bg; @border: @btn-disable-border) {
   &-disabled,
   &.disabled,
   &[disabled] {
@@ -16,7 +16,8 @@
     &:focus,
     &:active,
     &.active {
-      .button-color(@btn-disable-color; @btn-disable-bg; @btn-disable-border);
+      .button-color(@color; @background; @border);
+
       text-shadow: none;
       box-shadow: none;
     }
@@ -84,16 +85,26 @@
   }
   .button-disabled();
 }
-.button-variant-ghost(@color) {
-  .button-color(@color; transparent; @color);
+.button-variant-ghost(@color; @border: @color) {
+  .button-color(@color; transparent; @border);
   text-shadow: none;
   &:hover,
   &:focus {
-    .button-color(~`colorPalette('@{color}', 5) `; transparent; ~`colorPalette('@{color}', 5) `);
+    & when (@border = transparent) {
+      .button-color(~`colorPalette('@{color}', 5) `; transparent; transparent);
+    }
+    & when not(@border = transparent) {
+      .button-color(~`colorPalette('@{color}', 5) `; transparent; ~`colorPalette('@{color}', 5) `);
+    }
   }
   &:active,
   &.active {
-    .button-color(~`colorPalette('@{color}', 7) `; transparent; ~`colorPalette('@{color}', 7) `);
+    & when (@border = transparent) {
+      .button-color(~`colorPalette('@{color}', 7) `; transparent; transparent);
+    }
+    & when not(@border = transparent) {
+      .button-color(~`colorPalette('@{color}', 7) `; transparent; ~`colorPalette('@{color}', 7) `);
+    }
   }
   .button-disabled();
 }