This change turns quoted match to be case-sensitive (as before),
but not strictly full-string for the whole element's text.
This is a fix for a case where element contains text nodes and child elements:
```html
<div>text1<span>child node</span>text2</div>
```
We now match this div by `text="text1"` and `text="text2"`.
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.
This changes quoted text selector like `text="Foo Bar"` to perform
normalized whitespace match.
Most of the time users want to match some string visible on the page,
and that always means normalized whitespace.
We keep the case sensitivity and full-string vs substring difference
between quoted and unquoted matches.
We now default to `text` that does substring case-insensitive match
with normalized whitespace. `text-is` matches the whole string.
`matches-text` is renamed to `text-matches`.
This is a large rework of selectors:
- Each BrowserContext now has a separate Selectors instance that has its own registrations.
Most of them share a single sharedSelectors instance, but contexts created for a connected
browser have their own instance.
- Connected browser now gets a RemoteBrowser object that encapsulates Selectors and Browser.
This Selectors object is registered with the api selectors.
- Public selectors.register api iterates over all registered Selectors channels
and registers in each of them.
- createSelector testing method migrated to ElementHandle._createSelectorForTest.
