Ensure that explode($d, lowercase-string) produces list<lowercase-string> types

This specific distinction seems to be very important for Psalm, as `explode()` and
`lowercase-string` are used aggressively across the codebase.

Also, this change expands the baseline by a few entries, since some of the code locations
instide Psalm itself have un-checked list destructuring operations, as well as array
access calls on potentially undefined array keys produced by `explode()`, which were
previously just `list<string>`, and are now `array{0: string, 1?: string}`, which is
a bit more precise.

psalm-baseline.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<files psalm-version="dev-master@6fc9e50b9765d573db796e81522af759bc6987a5">
+<files psalm-version="dev-master@dbcfe62c5224603912c94c1eab5d7c31841ada82">
   <file src="examples/TemplateChecker.php">
     <PossiblyUndefinedIntArrayOffset>
       <code>$comment_block-&gt;tags['variablesfrom'][0]</code>
@@ -296,6 +296,12 @@
       <code>$b[$y]</code>
     </InvalidArrayOffset>
   </file>
+  <file src="src/Psalm/Internal/ExecutionEnvironment/GitInfoCollector.php">
+    <PossiblyUndefinedArrayOffset>
+      <code>$exploded[1]</code>
+      <code>$url</code>
+    </PossiblyUndefinedArrayOffset>
+  </file>
   <file src="src/Psalm/Internal/FileManipulation/PropertyDocblockManipulator.php">
     <PossiblyUndefinedIntArrayOffset>
       <code>$stmt-&gt;props[0]</code>
@@ -379,9 +385,9 @@
     <PossiblyInvalidArrayOffset>
       <code>$fixed_type_tokens[$i - 1]</code>
     </PossiblyInvalidArrayOffset>
-    <PossiblyUndefinedIntArrayOffset>
+    <PossiblyUndefinedArrayOffset>
       <code>$source_param_string</code>
-    </PossiblyUndefinedIntArrayOffset>
+    </PossiblyUndefinedArrayOffset>
   </file>
   <file src="src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeNodeScanner.php">
     <PossiblyUndefinedIntArrayOffset>
@@ -695,6 +701,8 @@
     <PossiblyUnusedMethod>
       <code>allFloatLiterals</code>
       <code>allFloatLiterals</code>
+      <code>hasLowercaseString</code>
+      <code>hasLowercaseString</code>
     </PossiblyUnusedMethod>
   </file>
   <file src="tests/Internal/Codebase/InternalCallMapHandlerTest.php">

stubs/CoreGenericFunctions.phpstub

@@ -728,6 +728,25 @@ function join($separator, array $array = []): string
  * @param non-empty-string $separator
  *
  * @return (
+ *     $string is lowercase-string
+ *         ? (
+ *             $limit is int<min, -2>
+ *                 ? array<empty, empty>
+ *                 : (
+ *                     $limit is int<0, 1>
+ *                         ? array{lowercase-string}
+ *                         : (
+ *                             $limit is 2
+ *                                 ? array{0: lowercase-string, 1?: lowercase-string}
+ *                                 : (
+ *                                     $limit is 3
+ *                                         ? array{0: lowercase-string, 1?: lowercase-string, 2?: lowercase-string}
+ *                                         : non-empty-list<lowercase-string>
+ *                                 )
+ *                         )
+ *                 )
+ *         )
+ *         : (
  *             $limit is int<min, -2>
  *                 ? array<empty, empty>
  *                 : (
@@ -744,6 +763,7 @@ function join($separator, array $array = []): string
  *                         )
  *                 )
  *         )
+ * )
  *
  * @psalm-flow ($string) -(array-assignment)-> return
  */