Use Mac system font instead of default monospace VSCode font

[larryqiann]

Under media-src/src/main.css, change the relevant section to the following (edit "1.3" per your preference - the Mac system font looks smaller than the default monospace VSCode font so I made it a bit bigger):

/* Use Apple system font stack while maintaining VS Code's font size */
.vditor .vditor-reset {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol' !important;
  font-size: calc(var(--vscode-editor-font-size) * 1.3) !important;
  line-height: var(--vscode-editor-line-height) !important;
}

This is not intended to be a pull request so this is probably not production ready, but it is nice to have the option for users that want this.

To build this, install:
-node
-yarn
-foy
-ts-node
-vsce

Then do yarn install in both the root directory AND the media-src directory

Then do "vsce package --no-yarn" in the root directory to build a VSIX. Uninstall the extension if installed, then click the three dots next to the refresh icon above the search bar in the Extensions pane and select install from VSIX.

Hopefully someone finds this useful!