R# atom label information lost in molfile if not handled by the RGP spec

[eloyfelix]

Describe the bug

related to #5763

We've encountered > 800 molfiles in ChEBI with R# atoms that are not handled by a M RGP entry.
RDKit replaces the R# with* and it is not possible to know, even with the mol.Debug() function that the original molfile had that R symbol/label there

To Reproduce

from rdkit import Chem

molfile = """
  Marvin  08301217132D          

  6  5  0  0  0  0            999 V2000
    7.3491   -3.6869    0.0000 O   0  0  0  0  0  0  0  0  0  0  0  0
    6.6346   -3.2744    0.0000 P   0  0  0  0  0  0  0  0  0  0  0  0
    5.9201   -3.6869    0.0000 O   0  5  0  0  0  0  0  0  0  0  0  0
    6.6346   -2.4494    0.0000 O   0  0  0  0  0  0  0  0  0  0  0  0
    6.8533   -4.0696    0.0000 O   0  5  0  0  0  0  0  0  0  0  0  0
    8.0660   -3.2844    0.0000 R#   0  0  0  0  0  0  0  0  0  0  0  0
  2  1  1  0  0  0  0
  3  2  1  0  0  0  0
  2  4  2  0  0  0  0
  2  5  1  0  0  0  0
  1  6  1  0  0  0  0
M  CHG  2   3  -1   5  -1
M  END
"""

mol = Chem.MolFromMolBlock(molfile)
mol.Debug()

Atoms:
	0 8 O chg: 0  deg: 2 exp: 2 imp: 0 hyb: 4 arom?: 0 chi: 0
	1 15 P chg: 0  deg: 4 exp: 5 imp: 0 hyb: 4 arom?: 0 chi: 0
	2 8 O chg: -1  deg: 1 exp: 1 imp: 0 hyb: 4 arom?: 0 chi: 0
	3 8 O chg: 0  deg: 1 exp: 2 imp: 0 hyb: 3 arom?: 0 chi: 0
	4 8 O chg: -1  deg: 1 exp: 1 imp: 0 hyb: 4 arom?: 0 chi: 0
	5 0 * chg: 0  deg: 1 exp: 1 imp: 0 hyb: 0 arom?: 0 chi: 0
Bonds:
	0 1->0 order: 1 conj?: 0 aromatic?: 0
	1 2->1 order: 1 conj?: 0 aromatic?: 0
	2 1->3 order: 2 conj?: 0 aromatic?: 0
	3 1->4 order: 1 conj?: 0 aromatic?: 0
	4 0->5 order: 1 conj?: 0 aromatic?: 0

Getting an R# instead of a * is quite important for ChEBI since they have a meaning in the ontology:
* = attaches to something
R = something attaches here

Expected behavior
Keep label info.

Configuration (please complete the following information):

• RDKit version: 2022.09.2
• If you are not using conda: how did you install the RDKit? pip