String.isBlank() not available under Java 8

Java 11 runtime methods have crept in to 2.11.5.0 - mostly due to our tests not being run under java 8 - problems in the files below were caught due to Jalview Test (jre8) failing to open the example file under Java 8.

(base) jprocter@M-000764 jalview % grep -r \.isBlank src
src/jalview/io/AnnotationFile.java: return isValidKey && !value.isBlank();
src/jalview/datamodel/BinaryNode.java: if (name != null && !name.isBlank())
src/mc_view/PDBChain.java: if (pdbid != null && !pdbid.isBlank())
src/mc_view/PDBChain.java: if (id != null && id.isBlank())