[Typescript-Angular] always generate package.json

This fixes the issue described in #14971, namely that when no npmName was provided then the instructions in the generate README fail because npm install complains that it cannot find a package.json.

In practice this PR provides a placeholder value for NPM_NAME when the user did not provide one. Consequently, a package.json is always generated.

To test this commit I generated a typescript-angular client (from any arbitrary openapi specification file) and ran the first 2 commands mentioned in the README, ie: npm install and npm run build.

• With this patch: both commands ran successfully
• Without this patch: the first command fails

---

An alternative I considered was to generate an ad hoc README rather than always providing a package.json. This could be achieved with a patch like this:

diff --cc modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptAngularClientCodegen.java
index 7675df8f18c,7675df8f18c..a32bc3229cb
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptAngularClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptAngularClientCodegen.java
@@@ -184,7 -184,7 +184,9 @@@ public class TypeScriptAngularClientCod
              throw new IllegalArgumentException("Invalid ngVersion: " + ngVersion + ". Only Angular v9+ is supported.");
          }
  
--        if (additionalProperties.containsKey(NPM_NAME)) {
++                boolean withNpmPackageGeneration = additionalProperties.containsKey(NPM_NAME);
++                additionalProperties.put("withNpmPackageGeneration", withNpmPackageGeneration);
++        if (withNpmPackageGeneration) {
              addNpmPackageGeneration(ngVersion);
          }
  
diff --cc modules/openapi-generator/src/main/resources/typescript-angular/README.mustache
index 3a65b9117ef,3a65b9117ef..b29e146da5b
--- a/modules/openapi-generator/src/main/resources/typescript-angular/README.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-angular/README.mustache
@@@ -1,5 -1,5 +1,6 @@@
  ## {{npmName}}@{{npmVersion}}
  
++{{#withNpmPackageGeneration}}
  ### Building
  
  To install the required dependencies and to build the typescript sources run:
@@@ -11,11 -11,11 +12,13 @@@ npm run buil
  ### publishing
  
  First build the package then run ```npm publish dist``` (don't forget to specify the `dist` folder!)
++{{/withNpmPackageGeneration}}
  
  ### consuming
  
--Navigate to the folder of your consuming project and run one of next commands.
++Navigate to the folder of your consuming project and run {{#withNpmPackageGeneration}}one of {{/withNpmPackageGeneration}}the next command{{#withNpmPackageGeneration}}s{{/withNpmPackageGeneration}}.
  
++{{#withNpmPackageGeneration}}
  _published:_
  

@@@ -23,6 -23,6 +26,7 @@@ npm install {{npmName}}@{{npmVersion}} 

  
  _without publishing (not recommended):_
++{{/withNpmPackageGeneration}}
  
  npm install PATH_TO_GENERATED_PACKAGE/dist.tgz --save

To be honest, I have very little experience in frontend (I'm more a backend dev) so I'm not sure which approach would be best. I'm proposing a PR which always generates package.json because it seems more consistent with what the javascript client generator is doing (and also because the generated README has several references to npmName)

Since this is related to typescript I guess I should ping @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero and @mkusaka

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