cmd/compile: add explanations to escape-analysis JSON/LSP logging
For 1.15.
From the test:
{"range":{"start":{"line":7,"character":13},"end":{...},"severity":3,"code":"leaks","source":"go compiler","message":"parameter z leaks to ~r2 with derefs=0","relatedInformation":[
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":13},"end":{...}},"message":"escflow: flow: y = z:"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":13},"end":{...}},"message":"escflow: from y = \u003cN\u003e (assign-pair)"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":13},"end":{...}},"message":"escflow: flow: ~r1 = y:"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":4,"character":11},"end":{...}},"message":"inlineLoc"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":13},"end":{...}},"message":"escflow: from y.b (dot of pointer)"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":4,"character":11},"end":{...}},"message":"inlineLoc"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":13},"end":{...}},"message":"escflow: from \u0026y.b (address-of)"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":4,"character":9},"end":...}},"message":"inlineLoc"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":13},"end":{...}},"message":"escflow: from ~r1 = \u003cN\u003e (assign-pair)"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":3},"end":...}},"message":"escflow: flow: ~r2 = ~r1:"},
{"location":{"uri":"file://T/file.go","range":{"start":{"line":9,"character":3},"end":...}},"message":"escflow: from return (*int)(~r1) (return)"}]}