Rollup merge of #139084 - petrochenkov:transpaque, r=davidtwco

hygiene: Rename semi-transparent to semi-opaque

"Semi-transparent" is just too damn long for a name, especially when used multiple times on a single line, it bothered me when working on #139083.

An optimist sees a macro as semi-opaque, a pessimist sees it as semi-transparent.
Or is it the other way round?

compiler/rustc_span/src/lib.rs

@@ -1117,7 +1117,7 @@ impl Span {
     /// Equivalent of `Span::mixed_site` from the proc macro API,
     /// except that the location is taken from the `self` span.
     pub fn with_mixed_site_ctxt(self, expn_id: ExpnId) -> Span {
-        self.with_ctxt_from_mark(expn_id, Transparency::SemiTransparent)
+        self.with_ctxt_from_mark(expn_id, Transparency::SemiOpaque)
     }
 
     /// Produces a span with the same location as `self` and context produced by a macro with the