Add internal getter for pure token URI

Fixes #3023

Add getter for pure token URI

- [x] Tests
- [x] Documentation
- [x] Changeset entry (run `npx changeset add`)

.changeset/hip-vans-crash.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`ERC721URIStorage`: added internal getter for retrieving token URI without base URI

contracts/mocks/token/ERC721URIStorageMock.sol

@@ -11,6 +11,10 @@ abstract contract ERC721URIStorageMock is ERC721URIStorage {
         return _baseTokenURI;
     }
 
+    function getPureTokenURI(uint256 tokenId) internal view returns (string memory) {
+        return _getPureTokenURI(tokenId);
+    }
+
     function setBaseURI(string calldata newBaseTokenURI) public {
         _baseTokenURI = newBaseTokenURI;
     }

contracts/token/ERC721/extensions/ERC721URIStorage.sol

@@ -43,6 +43,15 @@ abstract contract ERC721URIStorage is IERC4906, ERC721 {
         return super.tokenURI(tokenId);
     }
 
+    /**
+     * @dev gets the tokenURI of 'tokenId' without the baseURI
+     *
+     */
+
+    function _getPureTokenURI(uint256 tokenId) internal view virtual returns (string memory) {
+        return _tokenURIs[tokenId];
+    }
+
     /**
      * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
      *

test/token/ERC721/extensions/ERC721URIStorage.test.js

@@ -96,5 +96,11 @@ contract('ERC721URIStorage', function (accounts) {
       expect(await this.token.$_exists(firstTokenId)).to.equal(false);
       await expectRevert(this.token.tokenURI(firstTokenId), 'ERC721: invalid token ID');
     });
+
+    it('returns the pure base URI', async function () {
+      await this.token.setBaseURI(baseURI);
+
+      expect(await this.token.$_baseURI()).to.be.equal(baseURI);
+    });
   });
 });