Add support for the octet_length() SQL function, with low-level optimizations

that avoid loading large string content from disk when the argument to
octet_length() is a table column.

FossilOrigin-Name: fa5f77862c0fe0189aa4246a1e55bb7c537c28c436ec10b75f5fa141e5e4aff0

diff --cc manifest
index 078f72b8b23b0c677d21448ca15032411c5d3653,e8077c33a5b189390c87ed9c75e814e0ef7ae501..eff875a8362fea7847fd813b12c90db2295a8c6e
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Simplification\sto\sthe\sgetAndInitPage()\sroutine\sthat\sresults\sin\simproved\nperformance.
- D 2023-06-22T01:03:39.798
 -C Optimize\sthe\sargument\sto\sthe\soctet_length()\sfunction\sso\sthat\sit\sdoes\snot\nattempt\sto\sread\scontent\sfrom\sdisk.
 -D 2023-06-22T21:19:37.953
++C Add\ssupport\sfor\sthe\soctet_length()\sSQL\sfunction,\swith\slow-level\soptimizations\nthat\savoid\sloading\slarge\sstring\scontent\sfrom\sdisk\swhen\sthe\sargument\sto\noctet_length()\sis\sa\stable\scolumn.
++D 2023-06-23T11:10:13.280
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  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
  F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
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  # Remove this line to create a well-formed Fossil manifest.

diff --cc manifest.uuid
index 293cf2062a806751802b0e1a47d9769790b636c5,a671f73c0f7e05118fac947bf267dbc6d296827a..3e505065662f4ddd461d6f3e13cf33d43f07b3f4
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- 2e9734c2335d8c06fedc9f4cca02baaf326f7fa276bd464f3214f383715a48d6
 -8b8ea4e3f52d96cc217bd1fb27ca4a83489ef1f250756ed2f790d1b0ee529a3a
++fa5f77862c0fe0189aa4246a1e55bb7c537c28c436ec10b75f5fa141e5e4aff0