Inactive overload cache key

[BetsyMcPhail]

Fixes issue reported in RobotLocomotion/drake#11424 using suggestion similar to RobotLocomotion/drake#11424 (comment).

Upstream bug report: pybind#1922

This change will replace #32.

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This change is 

[BetsyMcPhail]

Reviewable status: 0 of 4 files reviewed, 1 unresolved discussion (waiting on @EricCousineau-TRI)

a discussion (no related file):
+@EricCousineau-TRI for review

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[EricCousineau-TRI]

with minor nits - thanks!

Reviewed 2 of 2 files at r1, 2 of 2 files at r2.
Dismissed @BetsyMcPhail from a discussion.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @BetsyMcPhail)

a discussion (no related file):
Testing locally, explicitly enabling the new test

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include/pybind11/pybind11.h, line 2431 at r2 (raw file):

    /* N.B. This uses `__qualname__.name` instead of `name`
       to resolve pybind11#1922. */
    auto full_name = type.attr("__qualname__").cast<std::string>() + "." + name;

nit Can you describe this as std::string, since it's a pretty straightforward type?

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include/pybind11/detail/internals.h, line 87 at r2 (raw file):

struct overload_hash {
    inline size_t operator()(const std::pair<const PyObject *, std::string>& v) const {
        size_t h1 = std::hash<const void *>()(v.first);

nit To minimize change, consider keeping the original semantics, size_t value = <first>; value ^= <second>; return value;?

[EricCousineau-TRI]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @BetsyMcPhail)

a discussion (no related file):

Previously, EricCousineau-TRI (Eric Cousineau) wrote…

Testing locally, explicitly enabling the new test

Done. Test passed locally.

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[BetsyMcPhail]

Reviewable status: 2 of 4 files reviewed, all discussions resolved (waiting on @EricCousineau-TRI)

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include/pybind11/pybind11.h, line 2431 at r2 (raw file):

Previously, EricCousineau-TRI (Eric Cousineau) wrote…

nit Can you describe this as std::string, since it's a pretty straightforward type?

Done

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include/pybind11/detail/internals.h, line 87 at r2 (raw file):

Previously, EricCousineau-TRI (Eric Cousineau) wrote…

nit To minimize change, consider keeping the original semantics, size_t value = <first>; value ^= <second>; return value;?

Done

[EricCousineau-TRI]

Reviewed 2 of 2 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved