Generate the TextMate sample renderings (#7762)

The images beside the samples were screenshots taken by hand, so they
drifted: they still showed `package Carbon api;`, syntax the language
dropped in 2024.

`render_sample.py` renders a sample the way the grammar in this
repository actually highlights it, using `tmlanguage.py`, a small
TextMate tokenizer. VS Code runs grammars under Oniguruma, which we
cannot depend on here, but this grammar uses no Oniguruma-only syntax,
so `re` runs its regexes unchanged and the two agree on every character
of every Carbon file in the repository. The output is SVG, so
regenerating needs nothing but Python, and a later grammar change gets a
same-path image diff showing what it did to real code.

The samples change where a construct left the language (`api`, `Carbon`
as the package name, `StringView`, `destructor`), refresh the
`keywords.carbon` inventory against `token_kind.def`, and add sections
for octal, raw and block literals, character literals, lambdas, and raw
identifiers. `interop.carbon` is new, covering inline C++. These are
highlighting fixtures rather than programs, so the deliberately invalid
lines stay.

Assisted-by: Claude Code

---------

Co-authored-by: Dana Jansens <danakj@orodu.net>

utils/textmate/Samples/functions_variables.carbon

@@ -37,3 +37,16 @@ fn F(ref a: A, const ref b: B);
 fn F() -> T;
 fn F() -> T.U { return val; }
 fn F() -> i32 => return val;
+
+// --- lambdas and positional parameters
+
+var explicit: auto = fn (x: i32) -> i32 { return x + 1; };
+var expression: auto = fn (x: i32) => x + 1;
+var positional: auto = fn { Print($0, $1, $42); };
+
+// --- raw identifiers
+
+r#class
+r#if
+r#i32
+var r#var: i32 = r#class;