Move reflection inside QuoteContext

[nicolasstucki]

Homogenize API used for macros and runtime staging. Support QuoteContext instead of Reflection as the implicit that macros take as parameter. We still a keep deprecated support for Reflection in macros. Note that the macros in scalatest, sourcecode and xml-interpolator did not need to change, they only get the warning suggesting to use QuoteContext.

[liufengyun]

LGTM

There are many places where we change import refl._ to import qctx.tasty._, which is a small regression in usability at first glance. This change is only justified by the hypothesis that most macros will be quote macros (which does not need the import), reflection macros are less common.

It would be good to have more evidence to support the hypothesis in real-world projects before deprecating the old syntax for reflection macros.

[liufengyun]

Nitpick : I'm not sure if tasty is a good name: (1) as a meta-programmer, I don't care about whether tasty or not, but only if the APIs are stable, useful and friendly; and it's easy to debug compiler crashes when using reflect API; (2) Reflection is more like an interface to compiler, reflect might be a better name.

[nicolasstucki]

In this case tasty should be read as the Typed AST API. I will add some documentation for it.

We cannot use reflect as it conflicts with the scala.reflect package and also the expectation of the users that know about scala.reflect. Calling scala.tasty.Reflection has already proven to lead the confusion and we should probably also rename it.

[nicolasstucki]

At least in scalatest it does not affect the code much, we can even remove one import per file.

[nicolasstucki]

Note that using import qctx.tasty._ instead of import refl._ is a necessary consequence of having a division of concerns between QuoteContext and Reflect. The latter contains the APIs related with TASTy trees while the first contains the APIs needed specifically for quotes and splices.