Format interpolated expressions as single line (#1247)

This forces iterpolated expressions to be single-line, so that newline
literals within the bounds of two string delimiters can be seen as
verbatime newlines in the resulting string.

Edge case: in the case of a line comment, it's not possible to keep
this as a single line expression.
These are kept as multi-line expressions.

Also:

* Remove `ForceWrap`, this node is not used.
* Rename `StringConstant` -> `StringChars`

pkl-formatter/src/test/files/FormatterSnippetTests/input/single-line-strings.pkl

@@ -0,0 +1,7 @@
+foo1 = "some string"
+
+foo2 = "some string with \( new { x = 1; y = 2 }) interpolation"
+
+foo3 = "some reeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaally long string with \( new { x = 1; y = 2 } ) interpolation"
+
+foo4 = "some reeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaally long string with \( foo.bar.baz() ) qualified access"

pkl-formatter/src/test/files/FormatterSnippetTests/input/string-interpolation.pkl

@@ -0,0 +1,51 @@
+prop1 =
+  """
+  asd \(new { bar = 1 }) asd
+  """
+
+prop2 =
+  """
+  \(let (bar = 15) bar + new { qux = 15 }.toString())
+  """
+
+prop3 =
+  """
+  \(new {
+    // some comment
+    foo = 1
+    
+    // some comment
+    bar = 2
+  })
+  """
+
+prop4 =
+  """
+  \(1 + /* block comment */ 2)
+  """
+
+prop5 =
+  """
+  \("""
+  foo
+  bar
+  baz
+  """)
+  """
+
+prop6 = "\(// some line comment
+  /* some block comment */
+  "\("""
+    one
+    two
+    three
+    """)"
+  // some line comment again
+)"
+
+prop7 = "\(
+5
+// trailing line comment
+)"
+
+prop8 = "\(new { foo = 1 bar = 2 baz = 3 })"

pkl-formatter/src/test/files/FormatterSnippetTests/output/multi-line-strings.pkl

@@ -1,8 +1,6 @@
 foo =
   """
-  asd \(new {
-    bar = 1
-  }) asd
+  asd \(new { bar = 1 }) asd
   """
 
 bar =

pkl-formatter/src/test/files/FormatterSnippetTests/output/single-line-strings.pkl

@@ -0,0 +1,9 @@
+foo1 = "some string"
+
+foo2 = "some string with \(new { x = 1; y = 2 }) interpolation"
+
+foo3 =
+  "some reeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaally long string with \(new { x = 1; y = 2 }) interpolation"
+
+foo4 =
+  "some reeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaally long string with \(foo.bar.baz()) qualified access"

pkl-formatter/src/test/files/FormatterSnippetTests/output/string-interpolation.pkl

@@ -0,0 +1,52 @@
+prop1 =
+  """
+  asd \(new { bar = 1 }) asd
+  """
+
+prop2 =
+  """
+  \(let (bar = 15) bar + new { qux = 15 }.toString())
+  """
+
+prop3 =
+  """
+  \(new {
+    // some comment
+    foo = 1
+
+    // some comment
+    bar = 2
+  })
+  """
+
+prop4 =
+  """
+  \(1 + /* block comment */ 2)
+  """
+
+prop5 =
+  """
+  \("""
+  foo
+  bar
+  baz
+  """)
+  """
+
+prop6 =
+  "\( // some line comment
+  /* some block comment */
+  "\("""
+  one
+  two
+  three
+  """)"
+  // some line comment again
+  )"
+
+prop7 =
+  "\(5
+  // trailing line comment
+  )"
+
+prop8 = "\(new { foo = 1; bar = 2; baz = 3 })"