[Syntax] test diagnostics in Lexer with libSyntax

[omochi]

To test diagnostics in Lexer with libSyntax,
add Diags arguments to swift::tokenize and swift:tokenizeWithTrivia.
"with libSyntaxmeansTriviaRetentionMode::WithTrivia` in Lexer.

I updated swift-syntax-test.cpp to passing Diags from getTokensFromFile into tokenizeWithTrivia.
It makes doFullLexRoundTrip and doDumpRawTokenSyntax are print diagnostics to stderr.

To keep compatibility,
I changed some Diags.hadAnyError() ? EXIT_FAILURE : EXIT_SUCCESS lines to just EXIT_SUCCESS.
Because, in previous Diags exists but not used so never had error.

And I add test case to check this.
To emit embedded nul character warnings,
I use little trick to make source code which is embedded nul.

This warning comes from standard Lexer logic and shared with WithTrivia and WithoutTrivia.
The purpose of this test case is checking testing of diagnostics mechanism through tokenizeWithTrivia.

In lexer_invalid_nul.swift,
tr '\132' '\0' means to change character Z to nul character.
To avoid replace character in argument of tr itself,
it uses octal form of Z , is \132.

I planned to implement some diagnostics in Lexer which already exists with WithoutTrivia but not exists WithTrivia.
This PR also prepares to this my plan.

[rintaro]

@swift-ci Please smoke test

[rintaro]

To keep compatibility,
I changed some Diags.hadAnyError() ? EXIT_FAILURE : EXIT_SUCCESS lines to just EXIT_SUCCESS.
Because, in previous Diags exists but not used so never had error.

It's unfortunate this Diags hadn't been used. I'm OK with this for now though.

[rintaro]

CC: @shahmishal https://ci.swift.org/job/swift-PR-Linux-smoke-test/4826/console

Build timed out (after 300 minutes). Marking the build as failed.

[rintaro]

@swift-ci Please smoke test Linux platform