Don't show undefined variable errors depending on context

[fbricon]

If a template checks a variable exists in a given context, eg. an if or for block, validation should know the variable exists and therefore should not complain about undefined variables.eg.

[angelozerr]

To check if an object part is optional you can use ObjectPart#isOptional();

It's the first step to remove the error from name?? in #if

For the second error, {name}, the main idea is to store in a list all optional part in

quarkus-ls/qute.ls/com.redhat.qute.ls/src/main/java/com/redhat/qute/services/QuteDiagnostics.java

Line 87 in b3d1031

private class ResolutionContext extends HashMap<String, ResolvedJavaTypeInfo> {

You will need to ad SectionKinf.IF in

quarkus-ls/qute.ls/com.redhat.qute.ls/src/main/java/com/redhat/qute/services/QuteDiagnostics.java

Line 347 in b3d1031

return sectionKind == SectionKind.EACH || sectionKind == SectionKind.FOR || sectionKind == SectionKind.LET

to create an instance of ResolutionContext.