Replace pickling of sub matches with an annotation

[EugeneFlesselle]

No description provided.

[sjrd]

This is not the usual modus operandi. What is calling for this change? There is nothing more permanent than a temporary solution.

[EugeneFlesselle]

This is not the usual modus operandi. What is calling for this change?

What would the modus operandi be (for an experimental feature in a new minor version)?
The intention was to avoid changing the TastyFormat for an experimental feature. The use of annotations is imitating:

scala3/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

Lines 861 to 863 in ee2f641

	if flags.is(Into) then
	// Temporary measure until we can change TastyFormat to include an INTO tag
	pickleAnnotation(sym, mdef, Annotation(defn.SilentIntoAnnot, util.Spans.NoSpan))

[sjrd]

The modus operandi is you just change the TASTy format to what you expect will look like the final version. That's why we have an experimental number in the TASTy version number.