This patch makes Splash correctly highlight associated types within
protocol declarations. Like other declarations, typed declared using
the `associatedtype` keyword should not be highlighted.
Previously, the last protocol would be treated as a function call (Splash
thought it was a call with trailing closure syntax, rather than the opening
of a type definition). This patch fixes that by verifying that the code
checking for constraints inside a generic type definition is in fact looking
at a generic, rather than something else.
Swift enables the use of keywords as function names, and we want those
to be treated as plain text (like other function names) rather than as
keywords. Some keywords require escaping using back-ticks, and this
patch accounts for both of those variations.
This patch fixes syntax highlighting for the following scenario:
```
Type<GenericType>.call()
```
Highlighting generic types is especially tricky, since we want them to
be highlighted when appearing at the call site, like above - but we don’t
want to highlight them when they are being declared. Hopefully with this
fix all/most edge cases are covered.
