- add a searchable Insert Snippet Universal Locator provider

- support runtime locator provider registration and removal
- filter snippets with workspace-relative include/exclude globs
- add the remaining VS Code-compatible snippet variables
- support camelcase, pascalcase, snakecase, and kebabcase modifiers
- reuse the existing insertion flow for locator-selected snippets
- expand snippet parser and store test coverage
- update the implementation plan and C/C++ example snippets

Refs: SpartanJ/ecode#111

.ecode/c-cpp.code-snippets

@@ -1,57 +0,0 @@
-{
-	"Main Function": {
-		"scope": "c,cpp",
-		"prefix": ["main", "mainfn"],
-		"body": [
-			"int main(int argc, char** argv) {",
-			"\t${1:(void)argc;}",
-			"\t${2:(void)argv;}",
-			"\t$0",
-			"\treturn 0;",
-			"}"
-		],
-		"description": "Program entry point"
-	},
-	"Indexed For Loop": {
-		"scope": "c,cpp",
-		"prefix": ["fori", "for-index"],
-		"body": [
-			"for (${1:size_t} ${2:i} = 0; $2 < ${3:count}; ++$2) {",
-			"\t$0",
-			"}"
-		],
-		"description": "Indexed loop with linked iterator placeholders"
-	},
-	"Include Header": {
-		"scope": "c,cpp",
-		"prefix": "inc",
-		"body": "#include ${1|<stdio.h>,<stdlib.h>,<string.h>,\"header.h\"|}$0",
-		"description": "Include a common system header or a local header"
-	},
-	"Guard Clause": {
-		"scope": "c,cpp",
-		"prefix": "guard",
-		"body": [
-			"if (${1:condition}) {",
-			"\t${2:return;}",
-			"}",
-			"$0"
-		],
-		"description": "Early-return guard clause"
-	},
-	"C++ Class": {
-		"scope": "cpp",
-		"prefix": "class",
-		"body": [
-			"class ${1:${TM_FILENAME_BASE}} {",
-			"  public:",
-			"\t$1(${2});",
-			"\t~$1();",
-			"",
-			"  private:",
-			"\t$0",
-			"};"
-		],
-		"description": "Class named after the current file with linked placeholders"
-	}
-}