fix package.json#exports for types

[NullVoxPopuli]

Goal:

• get publint and arethetypeswrong happy without disabling checks

Motivation:

• using the latest 1.2.x release, I was running in to type errors -- likely due to a misunderstanding I had with the vast of array of goofiness TS likes to have between authoring format and output format (they're compiling with tsc)

How I tested:

• Get the lints happy in this repo after removing the disables
  • However, due to limitations in wasm-pack, we can't get around the FalseESM rule, because wasm-pack does not emit node code in the ESM format. The APIs used for the "standalone" build also do not exist in node, so we can't just use "standalone" for everything. The real fix here is probably in wasm-pack to make their output less weird / dated.
• Run local tests
• Check the index.html (npm start, since we don't have browser tests)
• I built the package here and yarn link
• go over to my content-tag PR on the glint repo in the template-imports workspace and yarn link content-tag
• run yarn build in the glint root and check for errors. (At the time of creating this PR there are no errors)

Things I encountered:

• with the currently published package

  File '/home/nvp/Development/OpenSource/emberjs/glint/node_modules/content-tag/index.d.cts' 
       is not a module. [2306]
  

  which like.. true, because we're using require it shouldn't be a module -- at least not an ESM one -- which is how I interpret this -- which may be wrong.
  In this PR I've just deleted the index.d.cts
  I think I had originally thought that the index.d.cts could help with the FalseESM rule, but it did not.

• return type of parse is an array, rather than a single object -- this was a bug when the types were introduced

• when trying to use standalone.js as the entrypoint for cjs, we correctly get an error from TS

  packages/environment-ember-template-imports/-private/environment/preprocess.ts:16:30 - error TS1479: 
    The current file is a CommonJS module whose imports will produce 'require' calls;
    however, the referenced file is an ECMAScript module and cannot be imported with 
    'require'. Consider writing a dynamic 'import("content-tag")' call instead.
    
    To convert this file to an ECMAScript module, change its file extension to '.mts', 
    or add the field `"type": "module"` to 
    '/home/nvp/Development/OpenSource/emberjs/glint/packages/environment-ember-template-imports/package.json'.
  
  16 import { Preprocessor } from 'content-tag';
                                  ~~~~~~~~~~~~~
  

[NullVoxPopuli]

browser was moved under import to reduce the complexity and repetition of having types under 3 separate entries.