fix(nx-plugin): generator and executor generators should work in js libs

[AgentEnder]

Current Behavior

nx g @nrwl/nx-plugin:generator and nx g @nrwl/nx-plugin:executor have hardcoded paths for generators.json / executors.json with fallbacks in place for angular-CLI named collections.

They also fail if there is no executors.json or generators.json collection present. This is different from the behavior of @nrwl/nx-plugin:migration, so it is corrected in this PR.

Expected Behavior

nx g @nrwl/nx-plugin:generator and nx g @nrwl/nx-plugin:executor read paths for collection files from package.json and create them if they are not present

Related Issue(s)

Community slack thread: https://nrwlcommunity.slack.com/...

Fixes #

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✅ Successfully ran 11 targets

• nx affected --target=e2e --base=b9012fa66ec172cc61d86ff8002a68457980de41 --head=bad9704031c9459589447f1bd8a34575e24c281e --exclude=e2e-storybook,e2e-react-native,e2e-detox --parallel=1
• nx affected --target=test --base=b9012fa66ec172cc61d86ff8002a68457980de41 --head=bad9704031c9459589447f1bd8a34575e24c281e --parallel=1
• nx affected --target=build --base=b9012fa66ec172cc61d86ff8002a68457980de41 --head=bad9704031c9459589447f1bd8a34575e24c281e --parallel=3
• nx affected --target=lint --base=b9012fa66ec172cc61d86ff8002a68457980de41 --head=bad9704031c9459589447f1bd8a34575e24c281e --parallel=3
• nx-cloud record -- yarn nx workspace-lint
• nx-cloud record -- yarn documentation
• nx build typedoc-theme
• nx-cloud record -- yarn depcheck
• nx-cloud record -- yarn check-commit
• nx-cloud record -- yarn nx format:check --base=b9012fa66ec172cc61d86ff8002a68457980de41 --head=bad9704031c9459589447f1bd8a34575e24c281e
• nx-cloud record -- yarn check-imports

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Name	Status	Preview	Updated
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