feat: add support for optional env var replacements in .npmrc

[aczekajski]

This solves problem described in #8335 in a backwards-compatible way.

This PR adds possibility to have env var replacements in .npmrc configs written as ${VAR?} which will cause them to get replaced with an empty string if the variable is not defined. Old behavior where undefined variables are left unreplaced is not changed.

References

Fixes #8335

[wraithgar]

I know linting checks for this but I also manually validated via https://devina.io/redos-checker

[owlstronaut]

Looks like a great feature! Just a couple nits

[owlstronaut]

Suggested change

	variable name they can be forced to evaluate to an empty string instead.For
	variable name they can be forced to evaluate to an empty string instead. For

[owlstronaut]

Suggested change

	// optional "?" modifier can be used like this: ${ENV?} so in case of the variable being not defined, it evaluates into empty string
	// optional "?" modifier can be used like this: ${ENV?} so in case of the variable being not defined, it evaluates into empty string.

[owlstronaut]

Suggestion for a couple more tests here - and what do you think about adding a description, I find it way easier to read:

Suggested change

	t.equal(envReplace('\\${foo}', env), '${foo}')
	t.equal(envReplace('\\\\${foo}', env), '\\bar')
	t.equal(envReplace('\\\\\\${foo}', env), '\\${foo}')
	t.equal(envReplace('${baz}', env), '${baz}')
	t.equal(envReplace('\\${baz}', env), '${baz}')
	t.equal(envReplace('\\\\${baz}', env), '\\${baz}')
	t.equal(envReplace('\\${foo?}', env), '${foo?}')
	t.equal(envReplace('\\\\${foo?}', env), '\\bar')
	t.equal(envReplace('${baz?}', env), '')
	t.equal(envReplace('\\${baz?}', env), '${baz?}')
	t.equal(envReplace('\\\\${baz?}', env), '\\')
	t.equal(envReplace('${foo}', env), 'bar', 'replaces defined variable')
	t.equal(envReplace('${foo?}', env), 'bar', 'replaces defined variable with ? modifier')
	t.equal(envReplace('${foo}${bar}', env), 'barbaz', 'replaces multiple defined variables')
	t.equal(envReplace('${foo?}${baz?}', env), 'bar', 'replaces mixed defined/undefined variables with ? modifier')
	t.equal(envReplace('\\${foo}', env), '${foo}', 'escapes normal variable')
	t.equal(envReplace('\\\\${foo}', env), '\\bar', 'double escape allows replacement')
	t.equal(envReplace('\\\\\\${foo}', env), '\\${foo}', 'triple escape prevents replacement')
	t.equal(envReplace('${baz}', env), '${baz}', 'leaves undefined variable unreplaced')
	t.equal(envReplace('\\${baz}', env), '${baz}', 'escapes undefined variable')
	t.equal(envReplace('\\\\${baz}', env), '\\${baz}', 'double escape with undefined variable')
	t.equal(envReplace('\\${foo?}', env), '${foo?}', 'escapes optional variable')
	t.equal(envReplace('\\\\${foo?}', env), '\\bar', 'double escape allows optional replacement')
	t.equal(envReplace('${baz?}', env), '', 'replaces undefined variable with empty string when using ? modifier')
	t.equal(envReplace('\\${baz?}', env), '${baz?}', 'escapes undefined optional variable')
	t.equal(envReplace('\\\\${baz?}', env), '\\', 'double escape with undefined optional variable results in empty replacement')