editor: Fix double $ sign on completion accept in PHP (#34726)

Closes #33510 https://github.com/zed-extensions/php/issues/29

If certain language servers do not provide an insert/replace range, we
use `surrounding_word` as a fallback for that range, which internally
uses `word_characters`. It makes sense to use
`completion_query_characters` instead of `word_characters` to get that
range, because we use `completion_query_characters` to query completions
in the first place.

That means, for some hypothetical reason (e.g., if the Tailwind server
stops providing insert/replace ranges), we would correctly fall back to
the range "bg-blue-200^" instead of "200^", because
`completion_query_characters` includes "-" in this case.

For this particular fix, right now the default PHP language server
`phpactor` does not provide an insert/replace range, and hence
completion query character is used, which is `$` in this case.

Note that `$` isn't in word characters for reasons mentioned here:
https://github.com/zed-extensions/php/issues/14

Release Notes:

- Fixed an issue where accepting variable completion in PHP would result
in a double $ sign in the prefix.

crates/language/src/buffer.rs

@@ -3364,13 +3364,19 @@ impl BufferSnapshot {
 
     /// Returns a tuple of the range and character kind of the word
     /// surrounding the given position.
-    pub fn surrounding_word<T: ToOffset>(&self, start: T) -> (Range<usize>, Option<CharKind>) {
+    pub fn surrounding_word<T: ToOffset>(
+        &self,
+        start: T,
+        for_completion: bool,
+    ) -> (Range<usize>, Option<CharKind>) {
         let mut start = start.to_offset(self);
         let mut end = start;
         let mut next_chars = self.chars_at(start).take(128).peekable();
         let mut prev_chars = self.reversed_chars_at(start).take(128).peekable();
 
-        let classifier = self.char_classifier_at(start);
+        let classifier = self
+            .char_classifier_at(start)
+            .for_completion(for_completion);
         let word_kind = cmp::max(
             prev_chars.peek().copied().map(|c| classifier.kind(c)),
             next_chars.peek().copied().map(|c| classifier.kind(c)),