feat: support to preserve specific comments

[unbyte]

According to #1439 and #221 (comment), it seems that esbuild is not tend to supoort to preserve comments, but in our internal project we need to keep certain special placeholder comments for some tools to inject code, so I simply implement the basic feature we need and open this PR only to help others with the same needs get this patch easily.

To apply this patch:

$ curl -L https://github.com/evanw/esbuild/pull/2632.patch | git am

Example

CLI

$ esbuild --outfile=output.js --preserve-comments=\[PositionFor input.js

Input

/* [PositionForAppBegin] */
App({})
/* [PositionForAppEnd] */
/* should be removed */

Output

/* [PositionForAppBegin] */
App({});
/* [PositionForAppEnd] */

[benmccann]

Could this also be used to preserve all comments by passing something like .*? Storybook has a need to preserve comments as they're used for automatically generating documentation within Storybook. In the Svelte plugin, we need to first run any TypeScript through a compiler to convert to JavaScript so that the Svelte compiler can understand it. The fact that esbuild is removing comments is causing us major headaches (storybookjs/storybook#24096)