TSQL: fix statement delimitation

[jpers36]

Fixes #1581
Fixes #1555

The TSQL dialect allows for optional semicolon delimiters between statements. Since they are optional, we cannot rely on them to delimit the codebase. This code change removes all places where we assume semicolons will delimit and replaces them with optional references.

As part of this I discovered a bug with MetaSegment. If a MetaSegment leads a Sequence (as in FromExpressionSegment) it might be queried as to whether it is simple. The simple() function calls match() by default, which does not exist for MetaSegment. I added a simple() function override in MetaSegment which returns None.

TSQL changes:
+SelectClauseSegmentGrammar to override ANSI standard and remove delimitation logic that assumes the statements have been delimited
+SelectClauseElementSegment to override ANSI standard and remove GreedyUntil that assumes the statements have been delimited
+SelectClauseSegment to override ANSI standard and remove StartsWith logic that assumes the statements have been delimited
+DeleteStatementSegment to override ANSI standard and remove StartsWith logic that assumes the statements have been delimited
+FromClauseSegment to override ANSI standard and remove Delimited logic that assumes the statements have been delimited
+OrderByClauseSegment to override ANSI standard and remove StartsWith logic that assumes the statements have been delimited
Adjust SelectStatementSegment to allow for an optional semi-colon instead of an expected one.
Adjust CreateIndexStatementSegment to allow for an optional semi-colon instead of an expected one.
Adjust PivotUnpivotStatementSegment to remove StartsWith logic that assumes the statements have been delimited
Adjust CreateProcedureStatementSegment to remove StartsWith logic that assumes the statements have been delimited
Adjust CreateViewStatementSegment to allow for an optional semi-colon instead of an expected one.
Adjust CreateTableStatementSegment to allow for an optional semi-colon instead of an expected one.
Adjust TransactionStatementSegment to allow for an optional semi-colon instead of an expected one.
Adjust BatchSegment to clearly delineate logic between statements which can be bundled and statements which can't
Adjust BeginEndSegment to only include statements which can be bundled. As a result, we remove the reference to BatchSegment
+begin_end_no_semicolon test case to confirm that statements are parsed properly without semicolons
Adjust various test case YML scripts to reflect the changes above

meta.py changes:
import ParseContext, Optional, and List
Override simple() to return None instead of attempting to call match()

[codecov]

Codecov Report

Merging #1612 (48bf20f) into main (853ceef) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #1612   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          131       131           
  Lines         9184      9208   +24     
=========================================
+ Hits          9184      9208   +24     

Impacted Files	Coverage Δ
src/sqlfluff/core/parser/segments/meta.py	100.00% <100.00%> (ø)
src/sqlfluff/dialects/dialect_tsql.py	100.00% <100.00%> (ø)

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[tunetheweb]

Looks good. One suggestion.