Fix: pythonDatastoreVariableSymbols sometimes misses variables

[idillon-sfl]

I noticed pythonDatastoreVariableSymbols would give inconsistent results when the document is edited.

Steps to reproduce:

1. Create the following document:

   python() {
   d.getVar('DESCRIPTION')
   }

2. Restart VS Code (just making sure to have a clean state) and open the document.
3. Try to hover DESCRIPTION. It works.
4. Try to rename DESCRIPTION. It works.
5. Change the quotes:

   python() {
   d.getVar("DESCRIPTION")
   }

6. Try to hover DESCRIPTION. It still works.
7. Try to rename DESCRIPTION: The element can't be renamed (???)
8. Save the document and restart VS Code.
9. Try to rename DESCRIPTION: It works.

Not sure why this happens (bitBakeNodeAtPoint gives a different result after the edition), but here's a fix.

Problem has been understood: bitBakeNodeAtPoint uses the tree registered in uriToAnalyzedDocument. However, getSymbolsFromBitBakeTree is called before the new tree is registered. Therefore, if bitBakeNodeAtPoint is called whithin getSymbolsFromBitBakeTree, it will give a result from the previous tree. For that reason, it must be avoided.