Migrate most of the existing coverage tests over to run-coverage

tests/run-coverage/if_else.coverage

@@ -0,0 +1,41 @@
+    1|       |#![allow(unused_assignments, unused_variables)]
+    2|       |
+    3|      1|fn main() {
+    4|      1|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    5|      1|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    6|      1|    // dependent conditions.
+    7|      1|    let is_true = std::env::args().len() == 1;
+    8|      1|
+    9|      1|    let mut countdown = 0;
+   10|      1|    if
+   11|      1|        is_true
+   12|      1|    {
+   13|      1|        countdown
+   14|      1|        =
+   15|      1|            10
+   16|      1|        ;
+   17|      1|    }
+   18|       |    else // Note coverage region difference without semicolon
+   19|       |    {
+   20|      0|        countdown
+   21|      0|        =
+   22|      0|            100
+   23|       |    }
+   24|       |
+   25|       |    if
+   26|      1|        is_true
+   27|      1|    {
+   28|      1|        countdown
+   29|      1|        =
+   30|      1|            10
+   31|      1|        ;
+   32|      1|    }
+   33|       |    else
+   34|      0|    {
+   35|      0|        countdown
+   36|      0|        =
+   37|      0|            100
+   38|      0|        ;
+   39|      0|    }
+   40|      1|}
+