Tests: Add regression tests for the LibCpp preprocessor

Similarly to the LibCpp parser regression tests, these tests run the
preprocessor on the .cpp test files under
Userland/LibCpp/Tests/preprocessor, and compare the output with existing
.txt ground truth files.

Userland/Libraries/LibCpp/Tests/preprocessor/macro1.cpp

@@ -0,0 +1,2 @@
+#define ADD(x,y) x+y
+ADD(2,5);

Userland/Libraries/LibCpp/Tests/preprocessor/macro1.txt

@@ -0,0 +1,4 @@
+Integer  1:0-1:2 (2)
+Plus  1:0-1:2 (+)
+Integer  1:0-1:2 (5)
+Semicolon  1:8-1:8 (;)

Userland/Libraries/LibCpp/Tests/preprocessor/macro2.cpp

@@ -0,0 +1,3 @@
+#define M(x) String {x + "lo"}
+
+M("he" + "l")

Userland/Libraries/LibCpp/Tests/preprocessor/macro2.txt

@@ -0,0 +1,8 @@
+KnownType  2:0-2:0 (String)
+LeftCurly  2:0-2:0 ({)
+DoubleQuotedString  2:0-2:0 ("he")
+Plus  2:0-2:0 (+)
+DoubleQuotedString  2:0-2:0 ("l")
+Plus  2:0-2:0 (+)
+DoubleQuotedString  2:0-2:0 ("lo")
+RightCurly  2:0-2:0 (})

Userland/Libraries/LibCpp/Tests/preprocessor/macro3.cpp

@@ -0,0 +1,4 @@
+#define M(x, y, z) x y = z;
+
+M(Vector, vec, ({1,2}))
+

Userland/Libraries/LibCpp/Tests/preprocessor/macro3.txt

@@ -0,0 +1,11 @@
+KnownType  2:0-2:0 (Vector)
+Identifier  2:0-2:0 (vec)
+Equals  2:0-2:0 (=)
+LeftParen  2:0-2:0 (()
+LeftCurly  2:0-2:0 ({)
+Integer  2:0-2:0 (1)
+Comma  2:0-2:0 (,)
+Integer  2:0-2:0 (2)
+RightCurly  2:0-2:0 (})
+RightParen  2:0-2:0 ())
+Semicolon  2:0-2:0 (;)

Userland/Libraries/LibCpp/Tests/preprocessor/simple_define.cpp

@@ -0,0 +1,2 @@
+#define NUMBER 1337
+int x = NUMBER;

Userland/Libraries/LibCpp/Tests/preprocessor/simple_define.txt

@@ -0,0 +1,5 @@
+KnownType  1:0-1:2 (int)
+Identifier  1:4-1:4 (x)
+Equals  1:6-1:6 (=)
+Integer  1:8-1:13 (1337)
+Semicolon  1:14-1:14 (;)