This was making it hard to run the same benchmarks in a consistent way.

Release note: None

The .eg.go files had unnecessary imports of execgen, which is not
required in the runtime generated code, and in fact is suspicious.

Release note: None

This commit adds a new directive to execgen:

// execgen:inline

This directive causes a function that's annotated with it to be inlined
into all of its callers via AST transformation. This kind of inlining is
smarter than before - it permits arguments with names different from the
names of the function's formal parameters, for example.

This commit also changes the functions in distinct_tmpl to use this
directive instead of the manual templating method.

I think this is the only easy function to change. The rest have, at the
simple level of difficulty, static template-time parameters, and at a
harder level of difficulty, type parameters. Improving these cases
holistically should come next.

Release note: None