FCI platform name inconsistent between L1 and L2

[gerritholl]

Describe the bug

Platform names differ between L1 and L2 data for FCI.

To Reproduce

import hdf5plugin
from satpy import Scene

sc = Scene(
        filenames=["/media/nas/x23352/MTG/FCI/L1c/2024/12/17/12/W_XX-EUMETSAT-Darmstadt,IMG+SAT,MTI1+FCI-1C-RRAD-FDHSI-FD--CHK-BODY--DIS-NC4E_C_EUMT_20241217121419_IDPFI_OPE_20241217121007_20241217121017_N_JLS_O_0074_0001.nc"],
        reader="fci_l1c_nc")
sc.load(["vis_06"])
print(sc["vis_06"].attrs["platform_name"])

sc = Scene(
    filenames=["/media/nas/x23352/MTG/FCI/L2-cases/202412171200/W_XX-EUMETSAT-Darmstadt,IMG+SAT,MTI1+FCI-2-CLM--FD------NC4E_C_EUMT_20241217121531_L2PF_OPE_20241217120000_20241217121000_N__C_0073_0000.nc"],
    reader="fci_l2_nc")
sc.load(["cloud_state"])
print(sc["cloud_state"].attrs["platform_name"])

Expected behavior

I expect the platform name to be the same between L1 and L2.

Actual results

MTG-I1
MTI1

Environment Info:

• Satpy Version: main

Additional context

For L1c, we use a translation table to translate the source data (which have MTI1 in both cases) to WMO OSCAR values. This would suggest both should return Meteosat-12.

satpy/satpy/readers/fci_l1c_nc.py

Lines 197 to 209 in 7e31b15

	# Platform names according to the MTG FCI L1 Product User Guide,
	# EUM/MTG/USR/13/719113 from 2019-06-27, pages 32 and 124, are MTI1, MTI2,
	# MTI3, and MTI4, but we want to use names such as described in WMO OSCAR
	# MTG-I1, MTG-I2, MTG-I3, and MTG-I4.
	#
	# After launch: translate to METEOSAT-xx instead? Not sure how the
	# numbering will be considering MTG-S1 and MTG-S2 will be launched
	# in-between.
	_platform_name_translate = {
	"MTI1": "MTG-I1",
	"MTI2": "MTG-I2",
	"MTI3": "MTG-I3",
	"MTI4": "MTG-I4"}

There is no such translation for L2.

Related: #2994.