Feature/web/sticky tool (Tencent#1244)

* feat: 部分样式

* feat: 尝试百分比尺寸

* feat: 完善css

* feat: 样式调整

* fix: 删除wxss文件

* fix: lint

* fix: 改用全局变量

* feat: 修改布局方式

* feat: 暂存尝试联动backtop

* feat: 初始化sticky-tool demo文档

* chore: update description

* fix: lint:fix

* fix: lint:fix

* fix: 颜色修复

* feat: 添加hover动画

* feat: 完善动画

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Co-authored-by: yiranwu <yiranwu@tencent.com>
Co-authored-by: yuyang <uyarnchen@gmail.com>

style/web/components/sticky-tool/_mixin.less

@@ -6,6 +6,7 @@
     text-align: center;
     font-size: @sticky-item-font-size;
     color: @sticky-item-text-color;
+    transition: @sticky-item-bg-color-transition;
 
     &:hover {
       cursor: pointer;

style/web/components/sticky-tool/_var.less

@@ -36,6 +36,7 @@
 @sticky-item-text-color: @text-color-secondary;
 @sticky-item-icon-size: @icon-l;
 @sticky-item-icon-color: @text-color-primary;
+@sticky-item-bg-color-transition: background-color @anim-duration-base linear;
 
 // sticky-tool type=normal
 @sticky-item-size-normal: @comp-size-xxxl;