Implementation of basic data flow analysis for PowerPC (#212)

* WIP implementation

* * Move flow analysis to dedicated file
* Show string constants inline
* Handle calls to MWCC "sled" helpers which otherwise disrupt flow analysis

* Run cargo insta review

* Apply clippy feedback

* Update more tests.

* Remove std use from ppc flow analysis

* Try to make wasm build work again

* More test changes

* Probably last wasm fix

* Formatting

* Fix WASM

* One more clippy thing

* Fixed display of float constants in a LFS or LFD instruction in case where there is a branch to the subsequent instruction with a different register value.

* On lines with a reloc, only hide Symbol type data flow values rather than all data flow values.

* Formatting

objdiff-core/tests/snapshots/arch_arm__read_arm.snap

@@ -1954,4 +1954,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_arm__read_thumb.snap

@@ -3826,4 +3826,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_mips__read_mips.snap

@@ -1490,4 +1490,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_ppc__read_extab.snap

@@ -548,4 +548,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_ppc__read_ppc.snap

@@ -581,4 +581,5 @@ Object {
     ),
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_x86__read_x86.snap

@@ -207,4 +207,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_x86__read_x86_64.snap

@@ -1574,4 +1574,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_x86__read_x86_jumptable.snap

@@ -311,4 +311,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }

objdiff-core/tests/snapshots/arch_x86__read_x86_local_labels.snap

@@ -160,4 +160,5 @@ Object {
     split_meta: None,
     path: None,
     timestamp: None,
+    flow_analysis_results: {},
 }