[llvm] [ObjectYAML][NFC] Hoist BBAddrMap yaml2obj encoder into a shared helper (PR #205991)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `llvm` at step 6 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/48392

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-flang) failure: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
...
PASS: Flang :: Lower/OpenMP/requires-usm.f90 (4768 of 4778)
PASS: Flang :: Driver/mcmodel.f90 (4769 of 4778)
PASS: Flang :: Transforms/debug-local-var.fir (4770 of 4778)
PASS: Flang :: Semantics/OpenMP/declare-reduction-operator-modfile-reexport.f90 (4771 of 4778)
PASS: Flang :: Driver/fopenmp.f90 (4772 of 4778)
PASS: Flang :: Semantics/numeric_storage_size.f90 (4773 of 4778)
PASS: Flang :: Driver/nostdlib.f90 (4774 of 4778)
PASS: Flang :: Driver/omp-driver-offload.f90 (4775 of 4778)
PASS: flang-Unit :: Optimizer/./FlangOptimizerTests/174/177 (4776 of 4778)
PASS: Flang :: Driver/linker-options.f90 (4777 of 4778)
command timed out: 1200 seconds without output running [b'ninja', b'check-flang'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=3608.118934

```

</details>

https://github.com/llvm/llvm-project/pull/205991