Source position improvement

[nicolasstucki]

Current state

• Trees encode their source in uniqueId. This encoding is fragile and may have caused some issues (see dotc: Error: requirement failed: array index too large, maximum is 2^30 - 1 #9738).
• Inlined tree
  • When typing contains the original call in call
  • After PostTyper we encode a reference to the top-level class of the inlined code in call. This contains a symbol from which we get the source.

Improvements

The idea is to only keep the source in each tree in a clean way.

• Add a source field in Tree
  • Is the overhead acceptable? Or find better encoding. (see Make source a field in Positioned nodes #9900)
• Drop Inline nodes in PostTyper
  1. Use tree sources to reposition for JSR-45 workaround (see Inliner.scala#L222 , Improve debugging support by implementing JSR-45 #9715, Reposition trees in erasure using source from tree #9954)
  2. Pickle/unpickle tree sources in TASTy
  3. Remove or repurpose YCheckPositions
• TASTy Reflect
  • Reinterpret Inlined as Blocks
  • Allow access to tree sources