Improve callspec coverage

[guardrex]

Addresses #35434 (comment)
Fixes #35436

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[guardrex]

I did some work with the table content to specify placeholders.

I think I'm done tinkering with this now 😄 ... but ...

I'll want to say if "EXPR" (probably changed to "{EXPRESSION}`) means regex? I assume that's right ... that it's regex.

[pavelsavara]

I'll want to say if "EXPR" (probably changed to "{EXPRESSION}`) means regex? I assume that's right ... that it's regex.

Most likely not regex, this probably just means you can do say "include namespace Bla but exclude class Foo"

[guardrex]

@pavelsavara ... I see. No further changes needed then. I have that as "+EXPR" and "-EXPR" here matching the original table.