Parse lifetime bounds in lifetime param into TypeBoundList

This mainly aids in error recovery but also makes it a bit easier to handle lifetime resolution.
While doing so it also came apparent that we were not actually lowering lifetime outlives relationships within lifetime parameter declaration bounds, so this fixes that.

crates/intern/src/symbol/symbols.rs

@@ -80,6 +80,7 @@ define_symbols! {
     self_ = "self",
     Self_ = "Self",
     tick_static = "'static",
+    tick_underscore = "'_",
     dollar_crate = "$crate",
     MISSING_NAME = "[missing name]",
     fn_ = "fn",