coverage: Flatten BcbMappingKind into mappings::CodeMapping

Now that branch and MC/DC mappings have been split out into separate types and
vectors, this enum is no longer needed, since it only represents ordinary
"code" regions.

(We can revisit this decision if we ever add support for other region kinds,
such as skipped regions or expansion regions. But at that point, we might just
add new structs/vectors for those kinds as well.)

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -2,7 +2,7 @@ use rustc_middle::mir;
 use rustc_span::{BytePos, Span};
 
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
-use crate::coverage::mappings::{BcbMapping, BcbMappingKind};
+use crate::coverage::mappings;
 use crate::coverage::spans::from_mir::SpanFromMir;
 use crate::coverage::ExtractedHirInfo;
 
@@ -17,14 +17,14 @@ pub(super) fn extract_refined_covspans(
     mir_body: &mir::Body<'_>,
     hir_info: &ExtractedHirInfo,
     basic_coverage_blocks: &CoverageGraph,
-    mappings: &mut impl Extend<BcbMapping>,
+    code_mappings: &mut impl Extend<mappings::CodeMapping>,
 ) {
     let sorted_spans =
         from_mir::mir_to_initial_sorted_coverage_spans(mir_body, hir_info, basic_coverage_blocks);
     let coverage_spans = SpansRefiner::refine_sorted_spans(sorted_spans);
-    mappings.extend(coverage_spans.into_iter().map(|RefinedCovspan { bcb, span, .. }| {
+    code_mappings.extend(coverage_spans.into_iter().map(|RefinedCovspan { bcb, span, .. }| {
         // Each span produced by the generator represents an ordinary code region.
-        BcbMapping { kind: BcbMappingKind::Code(bcb), span }
+        mappings::CodeMapping { span, bcb }
     }));
 }