Add Databricks as a distinct dialect

[WittierDinosaur]

Brief summary of the change made

This separates out Databricks as its own dialect. For now, it just changes the keyword distribution between reserved and unreserved, but we may want to move the databricks-specific stuff in a non-back-compatible way for 2.0
Fixes #4266

Are there any other side effects of this change that we should be aware of?

No

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[coveralls]

Pull Request Test Coverage Report for Build 4286916548

• 13 of 13 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 4285501323:	0.0%
Covered Lines:	17253
Relevant Lines:	17253

---

💛 - Coveralls

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (2f4001e) compared to base (b600627).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #4438   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          206       208    +2     
  Lines        15408     15417    +9     
=========================================
+ Hits         15408     15417    +9     

Impacted Files	Coverage Δ
src/sqlfluff/core/dialects/__init__.py	100.00% <ø> (ø)
src/sqlfluff/rules/L064.py	100.00% <ø> (ø)
src/sqlfluff/rules/capitalisation/CP02.py	100.00% <ø> (ø)
src/sqlfluff/dialects/dialect_databricks.py	100.00% <100.00%> (ø)
...c/sqlfluff/dialects/dialect_databricks_keywords.py	100.00% <100.00%> (ø)
src/sqlfluff/rules/L026.py	100.00% <100.00%> (ø)
src/sqlfluff/rules/L057.py	100.00% <100.00%> (ø)

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[alanmcruickshank]

Good idea. If there are differences between the two - then it's a good idea to split them. Still makes sense for one to depend on the other though 👍