Investigate if LE.tagAsHavingIgnoredMandatoryErrors(int) is incorrectly short circuiting lambda exception analysis

[srikanth-sankaran]

See

https://bugs.eclipse.org/bugs/show_bug.cgi?id=422489#c2
https://bugs.eclipse.org/bugs/show_bug.cgi?id=422516 and
https://bugs.eclipse.org/bugs/show_bug.cgi?id=422134 for some background on

org.eclipse.jdt.internal.compiler.ast.LambdaExpression.tagAsHavingIgnoredMandatoryErrors(int)

This routine is basically trying to offer a safety net in preventing us from entering the mine field of flow analysis in the presence of a lambda that didn't resolve properly.

But it could be causing some damage also: In

https://bugs.eclipse.org/bugs/show_bug.cgi?id=547231,

we run into an IProblem.ParameterMismatch and tag the lambda and all enclosing lambdas as having ignored mandatory errors preventing exception analysis and resulting in spurious unhandled exception errors.