[slachiewicz]

Fixes #1129. The Go flyweight generator's templates now produce what gofmt produces (tabs, top-level methods, aligned struct fields and const blocks, gofmt's layout for the ComputeLength parameters), following the struct generator's approach rather than shelling out to gofmt. For every schema under sbe-tool/src/test/resources and gocode/resources, gofmt of the previous output equals the new output byte for byte. That covers whitespace, redundant if parentheses and a lowercase float exponent.

Verified: gofmt -l over the generated flyweight code → empty (200 of 200 files listed before); the gocode flyweight packages and otf pass with gofmt -l in place of go fmt; ./gradlew :sbe-tool:test → 482 tests, 1 failure, GolangGeneratorTest.shouldHandleLowerCaseEnumValueReference, which fails on master too when it runs before a test that sets sbe.keyword.append.token.