perf: don't recompile escapeRegExp for every query (#8956)

Context: the query builder is pretty CPU intensive, and can be slow -
e.g. #3857

One of the things which makes this slow is `escapeRegExp` in the query
builder: we freshly construct the same RegExp once per
`replacePropertyName` invocation (many times per overall query!) and
since the RegExp itself is constant -- we can lift it out and construct
it once.

Over-all this saves about 8% on our query build times as measured by
 #8955.

src/query-builder/QueryBuilder.ts

@@ -24,6 +24,7 @@ import { EntityPropertyNotFoundError } from "../error/EntityPropertyNotFoundErro
 import { ReturningType } from "../driver/Driver"
 import { OracleDriver } from "../driver/oracle/OracleDriver"
 import { InstanceChecker } from "../util/InstanceChecker"
+import { escapeRegExp } from "../util/escapeRegExp"
 
 // todo: completely cover query builder with tests
 // todo: entityOrProperty can be target name. implement proper behaviour if it is.
@@ -701,12 +702,8 @@ export abstract class QueryBuilder<Entity> {
     /**
      * Replaces all entity's propertyName to name in the given statement.
      */
-    protected replacePropertyNames(statement: string) {
-        // Escape special characters in regular expressions
-        // Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Escaping
-        const escapeRegExp = (s: String) =>
-            s.replace(/[.*+\-?^${}()|[\]\\]/g, "\\$&")
 
+    protected replacePropertyNames(statement: string) {
         for (const alias of this.expressionMap.aliases) {
             if (!alias.hasMetadata) continue
             const replaceAliasNamePrefix = this.expressionMap

src/util/escapeRegExp.ts

@@ -0,0 +1,4 @@
+// Escape special characters in regular expressions
+// Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Escaping
+const ESCAPE_REGEXP = /[.*+\-?^${}()|[\]\\]/g
+export const escapeRegExp = (s: String) => s.replace(ESCAPE_REGEXP, "\\$&")