text/template/parse: Pos is wrong in FieldNodes like .A.B.C

[pjweinb]

$ go version
go version go1.15.6 darwin/amd64

The template string

{{if .A.B.C.D}}{{printf .Z.Y.X.W}}
{{.Moo.N.P}}{{end}}

parses as

ListNode at 0:0, 2 children
. IfNode at 0:5
. . BranchNode at 0:5
. . Pipe. PipeNode at 0:5, 0 vars, 1 cmds
. . Pipe. . CommandNode at 0:5, 1 children
. . Pipe. . . FieldNode at 0:7, [A B C D]
. . List. ListNode at 0:15, 3 children
. . List. . ActionNode at 0:17
. . List. . . PipeNode at 0:17, 0 vars, 1 cmds
. . List. . . . CommandNode at 0:17, 2 children
. . List. . . . . IdentifierNode at 0:17
. . List. . . . . FieldNode at 0:26, [Z Y X W]
. . List. . TextNode at 1:1, len 1
. . List. . ActionNode at 1:2
. . List. . . PipeNode at 1:2, 0 vars, 1 cmds
. . List. . . . CommandNode at 1:2, 1 children
. . List. . . . . FieldNode at 1:6, [Moo N P]
. TextNode at 3:1, len 1

The offsets in the FieldNodes are after the first identifier. That is, in {{.Moo.N.P}} on line 1, the offset is 6, not 2. (And the same for the other FieldNodes.) If there is only one identifier in the FieldNode, then the offset is correct.

[toothrot]

/cc @robpike @mvdan