Provide some support for template files, implementing most of
https://docs.google.com/document/d/1clKAywucZVBXvL_v4mMhLQXso59lmQPMk1gtSpkV-Xw
Template support is controlled by the option 'experimentalTemplateSupport'
which defaults to false.
Most of the code is in a new 'template' package. Implemented are
semantic tokens, diagnostics, definitions, hover, and references,
and there is a stub for completions.
This code treats all the template files of a package together, so as
to follow cross-references.
Change-Id: I793606d8a0c9e96a0c015162d68f56b5d8599294
Reviewed-on: https://go-review.googlesource.com/c/tools/+/297871
Run-TryBot: Peter Weinberger <pjw@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Trust: Peter Weinberger <pjw@google.com>