[llvm] [NFC][LLVM][TableGen] Use `decodeULEB128` for `OPC_SoftFail` emission (PR #136220)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `flang-x86_64-windows` running on `minipc-ryzen-win` while building `llvm` at step 8 "test-build-unified-tree-check-flang-rt".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/166/builds/1191

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

```
Step 8 (test-build-unified-tree-check-flang-rt) failure: test (failure)
******************** TEST 'flang-rt-Unit :: Runtime/./RuntimeTests.exe/2/8' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:C:\buildbot\flang-x86_64-windows\build\runtimes\runtimes-bins\flang-rt\unittests\Runtime\.\RuntimeTests.exe-flang-rt-Unit-4796-2-8.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=8 GTEST_SHARD_INDEX=2 C:\buildbot\flang-x86_64-windows\build\runtimes\runtimes-bins\flang-rt\unittests\Runtime\.\RuntimeTests.exe
--

Note: This is test shard 3 of 8.

[==========] Running 28 tests from 24 test suites.

[----------] Global test environment set-up.

[----------] 1 test from AllocatableTest

[ RUN      ] AllocatableTest.AllocateSourceZeroSize

[       OK ] AllocatableTest.AllocateSourceZeroSize (0 ms)

[----------] 1 test from AllocatableTest (0 ms total)



[----------] 1 test from AdjustLRTests/0, where TypeParam = <type>

[ RUN      ] AdjustLRTests/0.AdjustL

[       OK ] AdjustLRTests/0.AdjustL (0 ms)

[----------] 1 test from AdjustLRTests/0 (0 ms total)



[----------] 1 test from CharacterComparisonTests/2, where TypeParam = <type>

[ RUN      ] CharacterComparisonTests/2.CompareCharacters

[       OK ] CharacterComparisonTests/2.CompareCharacters (0 ms)

[----------] 1 test from CharacterComparisonTests/2 (0 ms total)



[----------] 1 test from ExtremumTests/2, where TypeParam = <type>

[ RUN      ] ExtremumTests/2.MaxTests

[       OK ] ExtremumTests/2.MaxTests (0 ms)

[----------] 1 test from ExtremumTests/2 (0 ms total)

...

```

</details>

https://github.com/llvm/llvm-project/pull/136220