refactor(core): use path toString function from @sanity/util/paths (

#5987)

### Description

When deriving search weights, we previously relied on a new `pathToString` function that replicated much of the functionality already implemented in the `toString` function from `@sanity/util/paths`. The one additional piece of functionality (handling segments that are `true`, `false`, or `null`) has now been implemented in #5986. Once merged, we can remove the redundant `pathToString` function and switch to the `toString` function from `@sanity/util/paths`.

### What to review

- Search requests are constructed correctly.

### Testing

There are tests for this functionality in `packages/sanity/src/core/search/common/__tests__/deriveSearchWeightsFromType.test.ts`.

packages/sanity/src/core/search/common/deriveSearchWeightsFromType.ts

@@ -1,4 +1,5 @@
 import {type CrossDatasetType, type SchemaType, type SearchConfiguration} from '@sanity/types'
+import {toString as pathToString} from '@sanity/util/paths'
 
 import {isRecord} from '../../util'
 import {type SearchPath, type SearchSpec} from './types'
@@ -19,7 +20,6 @@ const BASE_WEIGHTS: Record<string, Omit<SearchWeightEntry, 'path'>> = {
   _id: {weight: 1, type: 'string'},
   _type: {weight: 1, type: 'string'},
 }
-const GROQ_RESERVED_KEYWORDS = ['true', 'false', 'null']
 const builtInObjectTypes = ['reference', 'crossDatasetReference']
 
 const getTypeChain = (type: SchemaType | undefined): SchemaType[] =>
@@ -39,22 +39,6 @@ function isSchemaType(input: SchemaType | CrossDatasetType | undefined): input i
   return typeof input !== 'undefined' && 'name' in input
 }
 
-/**
- * Serialize field path for GROQ query.
- *
- * Reserved keywords, such as `null`, cannot be accessed using dot notation. These fields will
- * instead be serialized using square bracket notation.
- */
-function pathToString(...path: string[]): string {
-  const cleanPath = path.filter(Boolean)
-  return cleanPath.slice(1).reduce((nextPath, segment) => {
-    if (GROQ_RESERVED_KEYWORDS.includes(segment)) {
-      return `${nextPath}['${segment}']`
-    }
-    return `${nextPath}.${segment}`
-  }, cleanPath[0])
-}
-
 function getLeafWeights(
   schemaType: SchemaType | CrossDatasetType | undefined,
   maxDepth: number,
@@ -84,7 +68,7 @@ function getLeafWeights(
     )
     for (const objectType of objectTypes) {
       for (const field of objectType.fields) {
-        const nextPath = pathToString(path, field.name)
+        const nextPath = pathToString([path, field.name].filter(Boolean))
         results.push(...traverse(field.type, nextPath, depth + 1))
       }
     }