src: enable wrapping Napi namespace with custom namespace

[addaleax]

Enable support for a NAPI_CPP_CUSTOM_NAMESPACE that would wrap
the Napi namespace in a custom namespace.

This can be helpful when there are multiple parts of a compiled
shared library or executable that depend on node-addon-api,
but different versions of it. In order to avoid symbol conflicts
in these cases, namespacing can be used to make sure that the
linker would not merge definitions that the compiler potentially
generates for the node-addon-api methods.

[addaleax]

Eslint error: 
/home/runner/work/node-addon-api/node-addon-api/test/error_terminating_environment.js
  38:3  error  Parsing error: 'return' outside of function

that seems silly, since I didn’t touch that part, and it’s perfectly valid to do top-level return in Node.js?

[mhdawson]

LGTM

[mhdawson]

@addaleax

that seems silly, since I didn’t touch that part, and it’s perfectly valid to do top-level return in Node.js?

When we enabled eslint, it was set up to report on changed files. It has been awkward at times but avoided the need to do a massive change at one time.

Can you try adding

// eslint-disable-next-line

before the reported line to see if that quiets the report?

[NickNaso]

LGTM

[NickNaso]

First pass on CI:

Version	Job	Status
main	https://ci.nodejs.org/job/node-test-node-addon-api-new/5424/	✓
v17.x	https://ci.nodejs.org/job/node-test-node-addon-api-new/5425/	✓
v16.x	https://ci.nodejs.org/job/node-test-node-addon-api-new/5426/	✓
v14.x	https://ci.nodejs.org/job/node-test-node-addon-api-new/5427/	✓
v12.x	https://ci.nodejs.org/job/node-test-node-addon-api-new/5428/	X (failure solved with PR #1138)

[addaleax]

before the reported line to see if that quiets the report?

That doesn’t work because this is a parsing error, not a linting error.

I’ve opened #1141, that should avoid this issue in the future.