Enhance ALTER TABLE to support adding and removing NOT NULL and CHECK

constraints.

FossilOrigin-Name: 895498e4431e02cff65a5d96db22f0b0cb9c96aedf1e3cdcdeb3c34c6fec432b

diff --cc manifest
index 279e0a1b6905c95d313b055aebeab3b19a8dec99,2c1aa727a77d5b68724b18345a6ec7f57c1d3292..b2773d549f156ec951ea0a25c1566b71cb5ad8b1
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Fix\sthe\sQRF\sso\sthat\sit\somits\sthe\sclosing\stext\sfrom\sstyles\s"json"\sand\s"jobject"\nwhen\sthe\sresult\sset\sit\sempty.
- D 2025-11-21T11:00:29.560
 -C Use\ssqlite3MPrintf()\sinstead\sof\ssqlite3_mprintf()\sinternally\sin\salter.c,\nfor\simproved\sOOM\sreporting.
 -D 2025-11-20T11:06:58.496
++C Enhance\sALTER\sTABLE\sto\ssupport\sadding\sand\sremoving\sNOT\sNULL\sand\sCHECK\nconstraints.
++D 2025-11-21T14:15:56.853
  F .fossil-settings/binary-glob 61195414528fb3ea9693577e1980230d78a1f8b0a54c78cf1b9b24d0a409ed6a x
  F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
  F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
@@@ -2175,8 -2177,8 +2177,9 @@@ F tool/version-info.c 33d0390ef484b3b1c
  F tool/warnings-clang.sh bbf6a1e685e534c92ec2bfba5b1745f34fb6f0bc2a362850723a9ee87c1b31a7
  F tool/warnings.sh d924598cf2f55a4ecbc2aeb055c10bd5f48114793e7ba25f9585435da29e7e98
  F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
- P 3c40614285449df259a3444e36f888cfb5e782ea58287914f97f496ea61e9e9f
- R 72c70ba25f0ad378a1be121350d99310
 -P 8fafd4988bf1fa1aa799c2834dd31bebdd52e7ae8e68c0197ccb497eb9b1e5f6
 -R db1904a60d74ce682aea26b215aeb826
++P e1ba175124be83da4db6d5d4e583b9b3b7dcb82e983c6f185d590469dcdc3139 57555d75daa2ee8345f8329749841a322b3e57679e5c4899ef749c8bc814812d
++R a08830703de06847124f417f6313a8fd
++T +closed 57555d75daa2ee8345f8329749841a322b3e57679e5c4899ef749c8bc814812d
  U drh
- Z 8420ad8f8baca6e0e81bbb82a5393430
 -Z f97a43221f64e29debc08ffbb7442414
++Z c52ca5465c06951a7373da17d60cecb6
  # Remove this line to create a well-formed Fossil manifest.

diff --cc manifest.uuid
index 1bdbcfee9c2b769fa94310ad9c1439314ba30be7,d3eecd4c350673618cf379cc30de57c537126842..47c7899bd5d2113a0429e73ce47318d2ea9d1867
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- e1ba175124be83da4db6d5d4e583b9b3b7dcb82e983c6f185d590469dcdc3139
 -57555d75daa2ee8345f8329749841a322b3e57679e5c4899ef749c8bc814812d
++895498e4431e02cff65a5d96db22f0b0cb9c96aedf1e3cdcdeb3c34c6fec432b