feat: Add implicit casting to TypeSignature::String

[jonathanc-n]

Which issue does this PR close?

Closes #.

Rationale for this change

#13402 #13394 were running into some problems with implicit casting due to TypeSignature::String not dealing with implicit casting properly

What changes are included in this PR?

Added implicit casting to TypeSignature::String

Are these changes tested?

Yes

Are there any user-facing changes?

[Omega359]

Please remove the changes to regexp_match as that change adds in support for utf8view which breaks that function (see ci output). It's a much larger issue than those changes. See #11911 (comment) for some details.

[jonathanc-n]

Will fix this tommorow.

[jayzhan211]

DuckDB doesn't allow this query 🤔
Numeric string casting is quite confusing to me

D SELECT ltrim(12345, '1');
Binder Error: No function matches the given name and argument types 'ltrim(INTEGER_LITERAL, STRING_LITERAL)'. You might need to add explicit type casts.
	Candidate functions:
	ltrim(VARCHAR) -> VARCHAR
	ltrim(VARCHAR, VARCHAR) -> VARCHAR

LINE 1: SELECT ltrim(12345, '1');

Same with postgres

postgres=# SELECT ltrim(12345, '1');
ERROR:  function ltrim(integer, unknown) does not exist
LINE 1: SELECT ltrim(12345, '1');
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

[jayzhan211]

Mark this as draft as it is not ready for review