Support build.jbang

[fbricon]

JBang now support a new build.jbang descriptor, see jbangdev/jbang@731399a

Supporting build.jbang files involves several tasks:

• detect during JBang manual import (Eclipse)
• detect during JBang automatic import (JDT.LS)
• trigger JBangBuilder on change (Eclipse)
• trigger JBangBuilder on change (JDT.LS)
• report diagnostics (Eclipse)
• report diagnostics (JDT.LS)