This changes `text=` and `:text()` selectors to match the element when:
- it's combined text content matches the text;
- combined text content of any immediate child does not match the text.
This allows the following markup to match "Some bold and italics text":
`<div>Some <b>bold</b> and <i>italics</i> text</div>`.
For the reference, "combined text content" is almost equal to `element.textContent`,
but with some changes like using value of `<input type=button>` or ignoring `<head>`.
This also includes some caching optimizations, meaningful in complex matches
that involve multiple calls to the text engine.
Performance changes (measured on large page with ~25000 elements):
- `:has-text()` - 14% faster.
- `text=` - 50% faster.
- `:text()` - 0-35% slower.
- `:text-matches()` - 28% slower.
These methods are useful for verification in tests, e.g.
```js
expect(await page.isEnabled(':text("Remove All")')).toBe(false);
await page.click(':text("Add Item")');
expect(await page.isVisible('.item:text("new item")')).toBe(true);
expect(await page.isEnabled(':text("Remove All")')).toBe(true);
```
When parsing CSS, we assume everything is a valid CSS function,
unless it is in the list of custom functions. This way we'll parse
future CSS functions automatically.
This enables filling the input based on the connected label:
```html
<label for=target>Name</label><input id=target>
```
```js
await page.fill('text=Name', 'Alice');
```
We used to do fetch() to decode the file buffer. However, this is
blocked by strict CSP policy. Instead, we can use explicit
string -> bytes conversion, and trade performance for CSP compliance.
