treewide: handle preDistPhases __structuredAttrs-agnostically

Always specify the preDistPhases attribute as a list instead of a string.

Append elements to the preDistPhases Bash variable using appendToVar
instead of string or Bash array concatenation.

Handle element insertion before a specific element using string
substitution as before, but handle both structured and unstructured
attributes.

pkgs/development/interpreters/python/hooks/pytest-check-hook.sh

@@ -58,5 +58,5 @@ function pytestCheckPhase() {
 
 if [ -z "${dontUsePytestCheck-}" ] && [ -z "${installCheckPhase-}" ]; then
     echo "Using pytestCheckPhase"
-    preDistPhases+=" pytestCheckPhase"
+    appendToVar preDistPhases pytestCheckPhase
 fi

pkgs/development/interpreters/python/hooks/python-catch-conflicts-hook.sh

@@ -6,5 +6,5 @@ pythonCatchConflictsPhase() {
 }
 
 if [ -z "${dontUsePythonCatchConflicts-}" ]; then
-    preDistPhases+=" pythonCatchConflictsPhase"
+    appendToVar preDistPhases pythonCatchConflictsPhase
 fi

pkgs/development/interpreters/python/hooks/python-imports-check-hook.sh

@@ -18,5 +18,5 @@ pythonImportsCheckPhase () {
 
 if [ -z "${dontUsePythonImportsCheck-}" ]; then
     echo "Using pythonImportsCheckPhase"
-    preDistPhases+=" pythonImportsCheckPhase"
+    appendToVar preDistPhases pythonImportsCheckPhase
 fi

pkgs/development/interpreters/python/hooks/python-remove-bin-bytecode-hook.sh

@@ -13,5 +13,5 @@ pythonRemoveBinBytecodePhase () {
 }
 
 if [ -z "${dontUsePythonRemoveBinBytecode-}" ]; then
-    preDistPhases+=" pythonRemoveBinBytecodePhase"
+    appendToVar preDistPhases pythonRemoveBinBytecodePhase
 fi

pkgs/development/interpreters/python/hooks/sphinx-hook.sh

@@ -69,4 +69,4 @@ installSphinxPhase() {
     runHook postInstallSphinx
 }
 
-preDistPhases+=" buildSphinxPhase installSphinxPhase"
+appendToVar preDistPhases buildSphinxPhase installSphinxPhase

pkgs/development/interpreters/python/hooks/unittest-check-hook.sh

@@ -13,5 +13,5 @@ unittestCheckPhase() {
 
 if [ -z "${dontUseUnittestCheck-}" ] && [ -z "${installCheckPhase-}" ]; then
     echo "Using unittestCheckPhase"
-    preDistPhases+=" unittestCheckPhase"
+    appendToVar preDistPhases unittestCheckPhase
 fi