Unite icons (#1374)

## Launch Checklist

This removes the `@mdi` (material design icons) package and uses the
icons from `react-icons`.
The icons are not exactly the same, but have the same idea behind them.

 - [x] Briefly describe the changes in this PR.
- [x] Include before/after visuals or gifs if this PR includes visual
changes.
 - [x] Add an entry to `CHANGELOG.md` under the `## main` section.

Main changes can be found below.
Before:
<img width="580" height="780" alt="image"
src="https://github.com/user-attachments/assets/e3d5fc8a-bd59-48fe-bdae-31bb290749c8"
/>


After:

<img width="580" height="780" alt="image"
src="https://github.com/user-attachments/assets/bacdbdba-9e73-4bef-bd30-26fe946269c1"
/>

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/components/LayerEditorGroup.tsx

@@ -1,9 +1,5 @@
 import React from "react";
-import Icon from "@mdi/react";
-import {
-  mdiMenuDown,
-  mdiMenuUp
-} from "@mdi/js";
+import {MdArrowDropDown, MdArrowDropUp} from "react-icons/md";
 import {
   AccordionItem,
   AccordionItemHeading,
@@ -30,17 +26,9 @@ export default class LayerEditorGroup extends React.Component<LayerEditorGroupPr
         onClick={_e => this.props.onActiveToggle(!this.props.isActive)}
       >
         <AccordionItemButton className="maputnik-layer-editor-group__button">
-          <span style={{flexGrow: 1}}>{this.props.title}</span>
-          <Icon
-            path={mdiMenuUp}
-            size={1}
-            className="maputnik-layer-editor-group__button__icon maputnik-layer-editor-group__button__icon--up"
-          />
-          <Icon
-            path={mdiMenuDown}
-            size={1}
-            className="maputnik-layer-editor-group__button__icon maputnik-layer-editor-group__button__icon--down"
-          />
+          <span style={{flexGrow: 1, alignContent: "center"}}>{this.props.title}</span>
+          <MdArrowDropUp size={"2em"} className="maputnik-layer-editor-group__button__icon maputnik-layer-editor-group__button__icon--up"></MdArrowDropUp>
+          <MdArrowDropDown size={"2em"} className="maputnik-layer-editor-group__button__icon maputnik-layer-editor-group__button__icon--down"></MdArrowDropDown>
         </AccordionItemButton>
       </AccordionItemHeading>
       <AccordionItemPanel>