Use static LazyLocks for all constant regexes (#22225)

Release Notes:

- N/A

crates/html_to_markdown/src/markdown_writer.rs

@@ -1,7 +1,6 @@
-use std::cell::RefCell;
 use std::collections::VecDeque;
 use std::rc::Rc;
-use std::sync::OnceLock;
+use std::{cell::RefCell, sync::LazyLock};
 
 use anyhow::Result;
 use markup5ever_rcdom::{Handle, NodeData};
@@ -10,13 +9,14 @@ use regex::Regex;
 use crate::html_element::HtmlElement;
 
 fn empty_line_regex() -> &'static Regex {
-    static REGEX: OnceLock<Regex> = OnceLock::new();
-    REGEX.get_or_init(|| Regex::new(r"^\s*$").unwrap())
+    static REGEX: LazyLock<Regex> =
+        LazyLock::new(|| Regex::new(r"^\s*$").expect("Failed to create empty_line_regex"));
+    &REGEX
 }
 
 fn more_than_three_newlines_regex() -> &'static Regex {
-    static REGEX: OnceLock<Regex> = OnceLock::new();
-    REGEX.get_or_init(|| Regex::new(r"\n{3,}").unwrap())
+    static REGEX: LazyLock<Regex> = LazyLock::new(|| Regex::new(r"\n{3,}").unwrap());
+    &REGEX
 }
 
 pub enum StartTagOutcome {