web: fix esbuild issue with style sheets (#8856)

Getting ESBuild, Lit, and Storybook to all agree on how to read and parse stylesheets is a serious
pain. This fix better identifies the value types (instances) being passed from various sources in
the repo to the three *different* kinds of style processors we're using (the native one, the
polyfill one, and whatever the heck Storybook does internally).

Falling back to using older CSS instantiating techniques one era at a time seems to do the trick.
It's ugly, but in the face of the aggressive styling we use to avoid Flashes of Unstyled Content
(FLoUC), it's the logic with which we're left.

In standard mode, the following warning appears on the console when running a Flow:

```
Autofocus processing was blocked because a document already has a focused element.
```

In compatibility mode, the following **error** appears on the console when running a Flow:

```
crawler-inject.js:1106 Uncaught TypeError: Failed to execute 'observe' on 'MutationObserver': parameter 1 is not of type 'Node'.
    at initDomMutationObservers (crawler-inject.js:1106:18)
    at crawler-inject.js:1114:24
    at Array.forEach (<anonymous>)
    at initDomMutationObservers (crawler-inject.js:1114:10)
    at crawler-inject.js:1549:1
initDomMutationObservers @ crawler-inject.js:1106
(anonymous) @ crawler-inject.js:1114
initDomMutationObservers @ crawler-inject.js:1114
(anonymous) @ crawler-inject.js:1549
```

Despite this error, nothing seems to be broken and flows work as anticipated.

web/package-lock.json

@@ -17059,6 +17059,7 @@
         },
         "node_modules/tree-sitter-json": {
             "version": "0.20.2",
+            "hasInstallScript": true,
             "license": "MIT",
             "optional": true,
             "dependencies": {
@@ -17067,6 +17068,7 @@
         },
         "node_modules/tree-sitter-yaml": {
             "version": "0.5.0",
+            "hasInstallScript": true,
             "license": "MIT",
             "optional": true,
             "dependencies": {

web/src/elements/utils/ensureCSSStyleSheet.ts

@@ -1,8 +1,35 @@
 import { CSSResult, unsafeCSS } from "lit";
 
+const supportsAdoptingStyleSheets: boolean =
+    window.ShadowRoot &&
+    (window.ShadyCSS === undefined || window.ShadyCSS.nativeShadow) &&
+    "adoptedStyleSheets" in Document.prototype &&
+    "replace" in CSSStyleSheet.prototype;
+
+function stringToStylesheet(css: string) {
+    if (supportsAdoptingStyleSheets) {
+        const sheet = unsafeCSS(css).styleSheet;
+        if (sheet === undefined) {
+            throw new Error(
+                `CSS processing error: undefined stylesheet from string.  Source: ${css}`,
+            );
+        }
+        return sheet;
+    }
+
+    const sheet = new CSSStyleSheet();
+    sheet.replaceSync(css);
+    return sheet;
+}
+
+function cssResultToStylesheet(css: CSSResult) {
+    const sheet = css.styleSheet;
+    return sheet ? sheet : stringToStylesheet(css.toString());
+}
+
 export const ensureCSSStyleSheet = (css: string | CSSStyleSheet | CSSResult): CSSStyleSheet =>
-    typeof css === "string"
-        ? (unsafeCSS(css).styleSheet as CSSStyleSheet)
-        : css instanceof CSSResult
-          ? (css.styleSheet as CSSStyleSheet)
+    css instanceof CSSResult
+        ? cssResultToStylesheet(css)
+        : typeof css === "string"
+          ? stringToStylesheet(css)
           : css;