bpo-43853: Handle sqlite3_value_text() errors

[erlend-aasland]

• raise MemoryError if sqlite3_value_text() sets SQLITE_NOMEM
• use sqlite3_value_bytes() to find string length; must be called after sqlite3_value_text()
• replace PyUnicode_FromString with PyUnicode_FromStringAndSize() and let errors propagate

https://bugs.python.org/issue43853

[erlend-aasland]

@pablogsal, see top comment for a description of the changes.

Relevant SQLite docs: https://sqlite.org/c3ref/value_blob.html

• "As long as the input parameter is correct, these routines can only fail if an out-of-memory error occurs during a format conversion."
• "If an out-of-memory error occurs, then the return value from these routines is the same as if the column had contained an SQL NULL value. Valid SQL NULL returns can be distinguished from out-of-memory errors by invoking the sqlite3_errcode() immediately after the suspect return value is obtained and before any other SQLite interface is called on the same database connection."

We call the API's in the following order:

1. sqlite3_value_type() (the switch statement in line 556)
2. sqlite3_value_text() (case SQLITE_TEXT in line 563)
3. sqlite3_errcode()
4. sqlite3_value_bytes()

[miss-islington]

Thanks @erlend-aasland for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

[erlend-aasland]

Thanks for reviewing, Pablo!

[bedevere-bot]

GH-26534 is a backport of this pull request to the 3.10 branch.

[miss-islington]

Thanks @erlend-aasland for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

[miss-islington]

Sorry, @erlend-aasland and @pablogsal, I could not cleanly backport this to 3.9 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 006fd869e4798b68e266f5de89c83ddb531a756b 3.9

[erlend-aasland]

I'll fix the backport.

[bedevere-bot]

GH-27627 is a backport of this pull request to the 3.9 branch.