docs: headers for snippet prop section (#15745)

Closes #14020
Closes #15172

Author: Rich-Harris

documentation/docs/03-template-syntax/06-snippet.md

@@ -112,6 +112,8 @@ Snippets can reference themselves and each other ([demo](/playground/untitled#H4
 
 ## Passing snippets to components
 
+### Explicit props
+
 Within the template, snippets are values just like any other. As such, they can be passed to components as props ([demo](/playground/untitled#H4sIAAAAAAAAE3VS247aMBD9lZGpBGwDASRegonaPvQL2qdlH5zYEKvBNvbQLbL875VzAcKyj3PmzJnLGU8UOwqSkd8KJdaCk4TsZS0cyV49wYuJuQiQpGd-N2bu_ooaI1YwJ57hpVYoFDqSEepKKw3mO7VDeTTaIvxiRS1gb_URxvO0ibrS8WanIrHUyiHs7Vmigy28RmyHHmKvDMbMmFq4cQInvGSwTsBYWYoMVhCSB2rBFFPsyl0uruTlR3JZCWvlTXl1Yy_mawiR_rbZKZrellJ-5JQ0RiBUgnFhJ9OGR7HKmwVoilXeIye8DOJGfYCgRlZ3iE876TBsZPX7hPdteO75PC4QaIo8vwNPePmANQ2fMeEFHrLD7rR1jTNkW986E8C3KwfwVr8HSHOSEBT_kGRozyIkn_zQveXDL3rIfPJHtUDwzShJd_Qk3gQCbOGLsdq4yfTRJopRuin3I7nv6kL7ARRjmLdBDG3uv1mhuLA3V2mKtqNEf_oCn8p9aN-WYqH5peP4kWBl1UwJzAEPT9U7K--0fRrrWnPTXpCm1_EVdXjpNmlA8G1hPPyM1fKgMqjFHjctXGjLhZ05w0qpDhksGrybuNEHtJnCalZWsuaTlfq6nPaaBSv_HKw-K57BjzOiVj9ZKQYKzQjZodYFqydYTRN4gPhVzTDO2xnma3HsVWjaLjT8nbfwHy7Q5f2dBAAA)):
 
 ```svelte
@@ -144,6 +146,8 @@ Within the template, snippets are values just like any other. As such, they can
 
 Think about it like passing content instead of data to a component. The concept is similar to slots in web components.
 
+### Implicit props
+
 As an authoring convenience, snippets declared directly _inside_ a component implicitly become props _on_ the component ([demo](/playground/untitled#H4sIAAAAAAAAE3VSTa_aMBD8Kyu_SkAbCA-JSzBR20N_QXt6vIMTO8SqsY29tI2s_PcqTiB8vaPHs7MzuxuIZgdBMvJLo0QlOElIJZXwJHsLBBvb_XUASc7Mb9Yu_B-hsMMK5sUzvDQahUZPMkJ96aTFfKd3KA_WOISfrFACKmcOMFmk8TWUTjY73RFLoz1C5U4SPWzhrcN2GKDrlcGEWauEnyRwxCaDdQLWyVJksII2uaMWTDPNLtzX5YX8-kgua-GcHJVXI3u5WEPb0d83O03TMZSmfRzOkG1Db7mNacOL19JagVALxoWbztq-H8U6j0SaYp2P2BGbOyQ2v8PQIFMXLKRDk177pq0zf6d8bMrzwBdd0pamyPMb-IjNEzS2f86Gz_Dwf-2F9nvNSUJQ_EOSoTuJNvngqK5v4Pas7n4-OCwlEEJcQTIMO-nSQwtb-GSdsX46e9gbRoP9yGQ11I0rEuycunu6PHx1QnPhxm3SFN15MOlYEFJZtf0dUywMbwZOeBGsrKNLYB54-1R9WNqVdki7usim6VmQphf7mnpshiQRhNAXdoOfMyX3OgMlKtz0cGEcF27uLSul3mewjPjgOOoDukxjPS9rqfh0pb-8zs6aBSt_7505aZ7B9xOi0T9YKW4UooVsr0zB1BTrWQJ3EL-oWcZ572GxFoezCk37QLe3897-B2i2U62uBAAA)):
 
 ```svelte
@@ -165,6 +169,8 @@ As an authoring convenience, snippets declared directly _inside_ a component imp
 </Table>
 ```
 
+### Implicit `children` snippet
+
 Any content inside the component tags that is _not_ a snippet declaration implicitly becomes part of the `children` snippet ([demo](/playground/untitled#H4sIAAAAAAAAE3WOQQrCMBBFrzIMggql3ddY1Du4si5sOmIwnYRkFKX07lKqglqX8_7_w2uRDw1hjlsWI5ZqTPBoLEXMdy3K3fdZDzB5Ndfep_FKVnpWHSKNce1YiCVijirqYLwUJQOYxrsgsLmIOIZjcA1M02w4n-PpomSVvTclqyEutDX6DA2pZ7_ABIVugrmEC3XJH92P55_G39GodCmWBFrQJ2PrQAwdLGHig_NxNv9xrQa1dhWIawrv1Wzeqawa8953D-8QOmaEAQAA)):
 
 ```svelte
@@ -184,6 +190,8 @@ Any content inside the component tags that is _not_ a snippet declaration implic
 
 > [!NOTE] Note that you cannot have a prop called `children` if you also have content inside the component — for this reason, you should avoid having props with that name
 
+### Optional snippet props
+
 You can declare snippet props as being optional. You can either use optional chaining to not render anything if the snippet isn't set...
 
 ```svelte