feat: use FileSystemFileHandle to modify a file on the local filesystem (#965)

## Launch Checklist

<!-- Thanks for the PR! Feel free to add or remove items from the
checklist. -->


 - [x] Briefly describe the changes in this PR.
 - [x] Link to related issues.
- [x] Include before/after visuals or gifs if this PR includes visual
changes.
 - [ ] Write tests for all new functionality.
 - [x] Add an entry to `CHANGELOG.md` under the `## main` section.

## Changes

- This pull request makes use of the FileSystemFileHandle API to modify
a local file. No need to download it - just click save.
- I don't know how to cover this functionality by tests so I need
directions in case test coverage is required.
- The pull request adds
[@types/wicg-file-system-access](https://www.npmjs.com/package/@types/wicg-file-system-access)
as a new dev dependency which I am not really pleased about but can't
think of a way around it.

## Known Limitations

- The used File API is only available in when accessed from https or on
localhost.
- There is no visual indicator that the file has been saved. Previously
the browser showed it as a new download.

## Issue

- https://github.com/maplibre/maputnik/issues/964

## Screenshots

### Menu
<img
src="https://github.com/user-attachments/assets/dfcfc5c2-0019-4857-ba26-224b5598fc11"
/>

### Open modal
<img
src="https://github.com/user-attachments/assets/4e1293e8-16b6-4b86-925b-3bebb49d8ca6"
height="200px" />

### Save modal
<img
src="https://github.com/user-attachments/assets/4f10e2c0-2dd3-4726-a613-30e0406619b0"
height="200px" />

---------

Co-authored-by: Harel M <harel.mazor@gmail.com>

src/components/AppToolbar.tsx

@@ -2,7 +2,15 @@ import React from 'react'
 import classnames from 'classnames'
 import {detect} from 'detect-browser';
 
-import {MdFileDownload, MdOpenInBrowser, MdSettings, MdLayers, MdHelpOutline, MdFindInPage, MdLanguage} from 'react-icons/md'
+import {
+  MdOpenInBrowser,
+  MdSettings,
+  MdLayers,
+  MdHelpOutline,
+  MdFindInPage,
+  MdLanguage,
+  MdSave
+} from 'react-icons/md'
 import pkgJson from '../../package.json'
 //@ts-ignore
 import maputnikLogo from 'maputnik-design/logos/logo-color.svg?inline'
@@ -216,8 +224,8 @@ class AppToolbarInternal extends React.Component<AppToolbarInternalProps> {
             <IconText>{t("Open")}</IconText>
           </ToolbarAction>
           <ToolbarAction wdKey="nav:export" onClick={this.props.onToggleModal.bind(this, 'export')}>
-            <MdFileDownload />
-            <IconText>{t("Export")}</IconText>
+            <MdSave />
+            <IconText>{t("Save")}</IconText>
           </ToolbarAction>
           <ToolbarAction wdKey="nav:sources" onClick={this.props.onToggleModal.bind(this, 'sources')}>
             <MdLayers />