Migration of jsx files to tsx 2 (#850)

This is to continue the work of migrating all the jsx files into tsx
files.
The MO is basically described here: #848.

About 7 files to go...

src/components/_FunctionButtons.tsx

@@ -0,0 +1,58 @@
+import React from 'react'
+
+import InputButton from './InputButton'
+import {MdFunctions, MdInsertChart} from 'react-icons/md'
+import {mdiFunctionVariant} from '@mdi/js';
+
+type FunctionInputButtonsProps = {
+  fieldSpec?: any
+  onZoomClick?(...args: unknown[]): unknown
+  onDataClick?(...args: unknown[]): unknown
+  onExpressionClick?(...args: unknown[]): unknown
+};
+
+export default class FunctionInputButtons extends React.Component<FunctionInputButtonsProps> {
+  render() {
+    let makeZoomInputButton, makeDataInputButton, expressionInputButton;
+
+    if (this.props.fieldSpec.expression.parameters.includes('zoom')) {
+      expressionInputButton = (
+        <InputButton
+          className="maputnik-make-zoom-function"
+          onClick={this.props.onExpressionClick}
+          title="Convert to expression"
+        >
+          <svg style={{width:"14px", height:"14px", verticalAlign: "middle"}} viewBox="0 0 24 24">
+            <path fill="currentColor" d={mdiFunctionVariant} />
+          </svg>
+        </InputButton>
+      );
+
+      makeZoomInputButton = <InputButton
+        className="maputnik-make-zoom-function"
+        onClick={this.props.onZoomClick}
+        title="Convert property into a zoom function"
+      >
+        <MdFunctions />
+      </InputButton>
+
+      if (this.props.fieldSpec['property-type'] === 'data-driven') {
+        makeDataInputButton = <InputButton
+          className="maputnik-make-data-function"
+          onClick={this.props.onDataClick}
+          title="Convert property to data function"
+        >
+          <MdInsertChart />
+        </InputButton>
+      }
+      return <div>
+        {expressionInputButton}
+        {makeDataInputButton}
+        {makeZoomInputButton}
+      </div>
+    }
+    else {
+      return <div>{expressionInputButton}</div>
+    }
+  }
+}