import: go: Improve synopsis and description parsing.

import: go: Improve synopsis and description parsing.

* guix/import/go.scm (%strict-tokenizer?): Set parameter to #t.
(go-path-escape): Redefine to prevent inlining.
(http-get*): Replace by ...
(http-fetch*): this ...
(json-fetch*): New procedure.
(go.pkg.dev-info): Use http-fetch*.
(go-package-licenses): Rewrite in terms of go.pkg.dev-info.
(go-package-description): Likewise.
(go-package-synopsis): Likewise.
(fetch-go.mod): Use the memoized http-fetch*.
(parse-go.mod): Adjust to receive content as a string.
(fetch-module-meta-data): Adjust to use http-fetch*.
(go-module->guix-package): Adjust to the modified fetch-go.mod return value.
[inputs]: Use propagated inputs, which is the most common situations for Go
libraries.
[description]: Beautify description.
[licenses]: Do no check for #f.  The result of the license parsing is always a
list.
* tests/go.scm: Adjust following above changes.