Fix Debug Failure crash in combineValueAndTypeSymbols for mapped symbols

When a value symbol is a mapped symbol (from a mapped type like Omit<>),
combineValueAndTypeSymbols was losing the mapped symbol's check flags and
link properties (mappedType, keyType). This caused getTypeOfSymbol to
fall through to getTypeOfVariableOrParameterOrProperty, which crashed on
Debug.assertIsDefined(symbol.valueDeclaration) since mapped symbols
don't have a valueDeclaration.

The fix propagates CheckFlags.Mapped and the corresponding mapped symbol
links from the value symbol to the combined symbol, so getTypeOfSymbol
correctly dispatches to getTypeOfMappedSymbol.

Fixes #58534

Author: veeceey