Rollup merge of #129170 - artemagvanian:span-to-location, r=celinval

Add an ability to convert between `Span` and `visit::Location`

AFAIK, there is no way to create a `Location` from a `Span` because its only field is private. This makes it impossible to use visitor methods like `visit_statement` or `visit_terminator`.

This PR adds an implementation for`From<Span>` for `Location` to fix this.

r? ```@celinval```

compiler/stable_mir/src/mir/visit.rs

@@ -465,6 +465,22 @@ pub fn span(&self) -> Span {
     }
 }
 
+/// Location of the statement at the given index for a given basic block. Assumes that `stmt_idx`
+/// and `bb_idx` are valid for a given body.
+pub fn statement_location(body: &Body, bb_idx: &BasicBlockIdx, stmt_idx: usize) -> Location {
+    let bb = &body.blocks[*bb_idx];
+    let stmt = &bb.statements[stmt_idx];
+    Location(stmt.span)
+}
+
+/// Location of the terminator for a given basic block. Assumes that `bb_idx` is valid for a given
+/// body.
+pub fn terminator_location(body: &Body, bb_idx: &BasicBlockIdx) -> Location {
+    let bb = &body.blocks[*bb_idx];
+    let terminator = &bb.terminator;
+    Location(terminator.span)
+}
+
 /// Reference to a place used to represent a partial projection.
 pub struct PlaceRef<'a> {
     pub local: Local,