Added sectorization for VVHN, minor modify airport within VCL (#1070)

* Added sectorization for VVHN, minor modify airport within VCL

Added sector 1,2,3,4 for VVHN
Added Phnom Penh|VD FIR
Modified IATA for some airport within VCL
Added name for VVHN-1,2,3,4

* Apply suggestion from @Adrian2k

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Co-authored-by: Adrian Bjerke <[email protected]>

Author: AnTruongTV