ref: Split DWARF line records according to inlinees

[Swatinem]

Consider the following code:

  | fn parent() {
1 |   child1();
2 |   child2();
  | }
1 | fn child1() { child2() }
1 | fn child2() {}

we assume here that we transitively inline child2 all the way into parent.
but we only have a single line record for that whole chunk of code,
even though the inlining hierarchy specifies two different call sites

addr:    0x10 0x20 0x30 0x40 0x50
         v    v    v    v    v
# DWARF hierarchy
parent:  |-------------------|
child1:       |----|           (called from parent.c line 1)
child2:       |----|           (called from child1.c line 1)
                   |----|      (called from parent.c line 2)
# line records
         |----|         |----| (parent.c line 1)
              |---------|      (child2.c line 1)

[codecov-commenter]

Codecov Report

Merging #633 (65a71bf) into master (40a0e39) will increase coverage by 0.24%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #633      +/-   ##
==========================================
+ Coverage   71.09%   71.34%   +0.24%     
==========================================
  Files          96       96              
  Lines       18200    18341     +141     
==========================================
+ Hits        12940    13085     +145     
+ Misses       5260     5256       -4