[clangd] Enable hover on character literal.

[hokein]

Summary

In the initial hover expression patch (https://reviews.llvm.org/D72500), we
disabled all literals.

There is some value on running hover on character literals (e.g. see the
int value of the char).

[hokein]

clang-tools-extra/clangd/Hover.cpp

744

there may be some value to enable StringLiteral as well (e.g. see the length of the string), but it seems to work partially:

• auto char_ptr = "ab^c"; // fails
• char abc[] = "a^bc"; // works
• const char* ptr = "a^bc"; // fails"
• "a^bc"; // fails
• func("a^bc"); // fails

Looks like the reason is that EvaluateAsRValue fails on a lvalue StringLiteral. It'd require a bit of work to make it useful for common cases.

[hokein]

friendly ping, I think it would be nice to get it in before 14 release.

[kadircet]

thanks, lgtm!

clang-tools-extra/clangd/unittests/HoverTests.cpp

1254

s/,/;