feat: join field support relationships inside arrays (#9773)

### What?

Allow the join field to have a configuration `on` relationships inside
of an array, ie `on: 'myArray.myRelationship'`.

### Why?

This is a more powerful and expressive way to use the join field and not
be limited by usage of array data. For example, if you have a roles
array for multinant sites, you could add a join field on the sites to
show who the admins are.

### How?

This fixes the traverseFields function to allow the configuration to
pass sanitization. In addition, the function for querying the drizzle
tables needed to be ehanced.

Additional changes from https://github.com/payloadcms/payload/pull/9995:

- Significantly improves traverseFields and the 'join' case with a raw
query injection pattern, right now it's internal but we could expose it
at some point, for example for querying vectors.
- Fixes potential issues with not passed locale to traverseFields (it
was undefined always)
- Adds an empty array fallback for joins with localized relationships

Fixes #
https://github.com/payloadcms/payload/discussions/9643

---------

Co-authored-by: Because789 <thomas@because789.ch>
Co-authored-by: Sasha <64744993+r1tsuu@users.noreply.github.com>

test/joins/collections/Categories.ts

@@ -103,6 +103,12 @@ export const Categories: CollectionConfig = {
         },
       ],
     },
+    {
+      name: 'arrayPosts',
+      type: 'join',
+      collection: 'posts',
+      on: 'array.category',
+    },
     {
       name: 'singulars',
       type: 'join',

test/joins/collections/Posts.ts

@@ -69,5 +69,16 @@ export const Posts: CollectionConfig = {
         },
       ],
     },
+    {
+      name: 'array',
+      type: 'array',
+      fields: [
+        {
+          name: 'category',
+          type: 'relationship',
+          relationTo: categoriesSlug,
+        },
+      ],
+    },
   ],
 }

test/joins/int.spec.ts

@@ -94,6 +94,7 @@ describe('Joins Field', () => {
           category: category.id,
           camelCaseCategory: category.id,
         },
+        array: [{ category: category.id }],
       })
     }
   })
@@ -183,6 +184,15 @@ describe('Joins Field', () => {
     expect(docs[0].group.camelCaseCategory.group.camelCasePosts.docs).toHaveLength(10)
   })
 
+  it('should populate joins with array relationships', async () => {
+    const categoryWithPosts = await payload.findByID({
+      id: category.id,
+      collection: categoriesSlug,
+    })
+
+    expect(categoryWithPosts.arrayPosts.docs).toBeDefined()
+  })
+
   it('should populate uploads in joins', async () => {
     const { docs } = await payload.find({
       limit: 1,