go/printer, gofmt: line directives specifying columns must stay in place relative to next token

[griesemer]

gofmt changes the code

package p
/*line foo:10:12*/func g() /*line :20:13*/{}

to

package p

/*line foo:10:12*/
func g()/*line :20:13*/ {}

which changes the positions of some tokens. Generally, gofmt changes positions, but in the case of line directives specifying specific line and column values we want those values to remain stable.

See also #22662, #24143, and #24183.

[griesemer]

Moving to 1.13. No urgent need has come up for this.