[js/web] allow bundler import condition for not bundling wasm (#24014)
### Description
<!-- Describe your changes. -->
This gives a way for webapp developers to customize the bundler behavior
regarding whether to bundle the wasm.
To avoid treating ort-wasm-threaded-simd.jsep.mjs and
ort-wasm-threaded-simd.jsep.wasm as dependencies during the process of
bundler build, use import condition `onnxruntime-web-use-extern-wasm`.
For webpack:
```
module.exports = {
//...
resolve: {
conditionNames: ['onnxruntime-web-use-extern-wasm', 'import', 'module'],
},
};
```
For esbuild:
```
await esbuild.build({
//...
conditions: ['onnxruntime-web-use-extern-wasm', 'import', 'module'],
})
```
For rollup:
```
import { nodeResolve } from '@rollup/plugin-node-resolve';
export default {
//...
plugins: [nodeResolve({
exportConditions: ['onnxruntime-web-use-extern-wasm', 'import', 'module', 'development|production']
})]
};
```
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
- #24009
onnxruntime
78d91cdd - [js/web] allow bundler import condition for not bundling wasm (#24014)
